Low water consumption sand washing and grading integrated treatment process

Abstract

The present application relates to sand and gravel processing wastewater treatment technical field, disclose a kind of low water consumption sandstone cleaning and grading integrated treatment process, the process is added in closed-circuit circulating sand washing system Phosphorus-free dispersing complexing agent to mask polyvalent metal ions, inhibit system inorganic scale;The fine mud suspension obtained by cleaning and grading is injected into inorganic high molecular flocculants and inorganic sulfates in turn to build salting-out background;Then the slurry is introduced into the fluid mixing device with cross-section mutation and injected into hydrophobically modified polyacrylamide, using the flow field space gradient and shear rate change inside the equipment, induce polymer to occur hydrophobic association under salting-out background, form three-dimensional network shrink and extrude capillary combined water in fine mud floc;The slurry after treatment is separated by thickening and pressure filtration, and the filtrate is reused.The process solves the problems of easy scaling of high-salt circulating water and difficult dewatering of fine mud, reduces the water consumption and moisture content of the system.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology in sand and gravel processing, specifically to an integrated process for low-water-consumption sand and gravel washing and grading. Background Technology

[0002] In the current sand and gravel aggregate processing industry, to conserve water resources and meet environmental protection requirements for zero emissions, sand washing wastewater is typically treated using a closed-loop recycling system. However, as the system operates in a closed loop for longer periods, salts washed from the ore surface accumulate, leading to a continuous increase in the total dissolved solids concentration in the recycled water. In such high-salinity water, the accumulated calcium, magnesium, and other polyvalent metal ions readily crystallize and precipitate inside fluid pipelines and dewatering equipment, forming difficult-to-remove inorganic scale, severely affecting the system's flow capacity. Traditional scale prevention methods often rely on adding phosphorus-containing scale inhibitors, but this carries the risk of eutrophication due to bottom sediment or external drainage.

[0003] Meanwhile, the high-salinity closed system had a significant negative impact on the solid-liquid separation process of sand washing tailings. In this type of high-conductivity aqueous phase, the molecular chains of conventional polyacrylamide-based flocculants undergo configurational coiling due to electrostatic shielding, leading to a substantial decrease in the polymer's trapping and bridging capabilities. This reduced flocculation effect results in a large amount of capillary-bound water being trapped on the surface of fine sludge particles and within the flocs. Conventional gravity sedimentation and mechanical pressure filtration are insufficient to overcome the binding forces between water molecules and solid particles, failing to effectively remove this deep water. This situation not only results in a high moisture content in the final filter cake, increasing the difficulty of dry-piling solid waste disposal, but also means that a large amount of water resources are lost outside the system as bound water in the filter cake. To maintain the liquid level balance of the closed-loop system, a large amount of fresh water must be continuously added, making it difficult to achieve the truly low-water-consumption operation target. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-water-consumption integrated sand and gravel washing and grading process. This process solves the problems of existing sand and gravel washing processes where, under a closed-loop water system, the continuous accumulation of total dissolved solids leads to severe inorganic scaling on the equipment. At the same time, the high-salt environment causes conventional flocculants to become curled and fail, making it difficult to remove capillary bound water from the fine mud suspension. Ultimately, this results in a large consumption of fresh water and a high water content in the mud cake.

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] This invention provides an integrated process for low-water-consumption sand and gravel washing and grading, employing the following technical solution:

[0007] S1: Start the closed-loop circulation system for sand washing water and control the total dissolved solids in the circulating return water to maintain within the set range;

[0008] S2: Feed the muddy sand and gravel raw materials into the sand washing equipment, pump in the circulating return water, and add a phosphorus-free dispersing complexing agent to the sand washing water phase to adjust the mixed slurry system to be weakly alkaline, so as to target and mask the multivalent metal ions in the water phase and prevent the system from scaling.

[0009] S3: Classify the washed and stripped slurry to separate the fine mud suspension;

[0010] S4: Inorganic polymeric flocculant and inorganic sulfate are sequentially injected into the fine mud suspension to construct an inorganic micro-flocculation framework and a local high-concentration salting-out background;

[0011] S5: The treated fine mud suspension is passed into a fluid mixing device with a cross-sectional abrupt change, and hydrophobic modified polyacrylamide is injected before the variable cross-section inlet. The shear rate abrupt change and spatial gradient flow field inside the fluid mixing device are used to induce hydrophobic association and generate three-dimensional network contraction in the salting-out background, forcibly squeezing out the capillary bound water inside the fine mud flocs.

[0012] S6: The treated slurry is discharged into a thickening device for gravity settling, the underflow slurry is dewatered by pressure filtration, and the overflow water from the thickening device and the filtrate from the pressure filtration are returned to step S1 as circulating water.

[0013] By adopting the above technical solution, and through the synergistic operation of a phosphorus-free dispersing complexing agent, inorganic sulfate, hydrophobically modified polyacrylamide, and fluid mixing equipment with abrupt cross-sectional changes, this process effectively constructs a composite treatment system encompassing chemical masking, salting-out coagulation, and flow field induction, thereby achieving reduced system water consumption and deep mud-water separation. Addressing the challenge of inorganic scale formation in high-salinity closed-loop circulation systems, a phosphorus-free dispersing complexing agent is added to the weakly alkaline sand washing water phase. The polyhydroxycarboxylic acid ions in the agent's molecular structure directly undergo coordination complexation reactions with free calcium and magnesium ions in the aqueous phase, generating water-soluble five- or six-membered cyclic complexes. The macroscopic reaction formula can be expressed as: This chemical process transforms free alkaline earth metal ions, which are prone to scaling, into a stable dissolved state, thus inhibiting the formation of calcium carbonate and calcium sulfate scale at the source, and incidentally avoiding the secondary eutrophication problem caused by traditional phosphorus-containing agents.

[0014] After addressing scaling concerns, solid-liquid separation of the fine sludge suspension becomes crucial. Inorganic polymeric flocculants added to the system utilize charge neutralization and a net-sweeping effect to aggregate free fine sludge particles into an inorganic micro-flocculated framework with initial strength. Based on this, injected inorganic sulfates dissociate into high concentrations of sulfate ions in the local aqueous phase. These sulfate ions, through their strong hydration, capture free water molecules, thereby reducing the solubility of the macromolecular polymer in water and establishing a stable thermodynamic salting-out background. Subsequently, the sludge mixed with hydrophobically modified polyacrylamide enters a fluid mixing device with a rapidly narrowing cross-section. As the fluid passes through the rapidly narrowing physical boundary of the device, the high shear rate and spatial gradient forces generated internally overcome the steric hindrance of the polymer molecular chains, forcing the originally coiled hydrophobically modified polyacrylamide backbone to unwind and expose hydrophobic side groups. Influenced by the previously established high-concentration sulfate salting-out background, the repulsive force of water molecules against these non-polar hydrophobic groups increases dramatically. To reduce the interfacial free energy of the system, hydrophobic groups on adjacent polymer chains spontaneously undergo intermolecular association and cross-linking, intertwining to form a dense three-dimensional network structure. As this cross-linked network shrinks and solidifies, the capillary bound water and interstitial water that were originally trapped inside the inorganic micro-flocculation skeleton are squeezed by the mechanical network, detached from the solid surface, and released into the liquid phase, thus completing the stripping process of deep bound water from fine mud particles.

[0015] Preferably, in step S1, the total dissolved solids in the circulating return water are controlled to be stable at 3000-4000 mg / L, and the conductivity is maintained at 5000-6500 uS / cm; in step S2, the liquid-solid mass ratio in the sand washing equipment is controlled to be 0.5-0.8:1, and the pH value of the mixed slurry system is maintained at 8.5-9.0.

[0016] By adopting the above technical solution, the process allows and maintains the total dissolved solids in the system within a relatively high concentration range. This effectively utilizes the bulk dissolved salts from the leaching of the raw ore, using them as the source of ionic strength for subsequent salting-out processes, thereby reducing the consumption of added salt additives. Simultaneously, the established weakly alkaline environment ensures the dissociation state of the carboxylic acid groups in the phosphorus-free dispersing complexing agent, guaranteeing that its spatial coordination configuration and masking effectiveness are at a reasonable level.

[0017] Preferably, in step S2, the phosphorus-free dispersing complexing agent is composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:1.5-2.5, and its total effective mass concentration in the sand washing aqueous phase is controlled at 80-120 mg / L.

[0018] By adopting the above technical solution, sodium polyacrylate mainly provides lattice distortion and electrostatic repulsion dispersion, while sodium gluconate focuses on polyhydroxy specific chelation. When the two are mixed in a set ratio, they can maintain the complexation state of calcium and magnesium ions within a wide range of water hardness fluctuations, thus ensuring the suspension stability of the high mud content slurry system.

[0019] Preferably, in step S4, the inorganic polymeric flocculant is polyaluminum ferric silicate, and its effective dosage in the aqueous phase is 20-30 mg / L; the inorganic sulfate is anhydrous sodium sulfate, and its dosage is controlled so that the mass concentration increase of sulfate ions in the local aqueous phase reaches 250-350 mg / L.

[0020] The above technical solution was adopted, and polyaluminum ferric silicate was chosen because the polynuclear hydroxyl complexes it produces have strong destabilizing ability, which helps to form a dense mud-flocculation structure. Using anhydrous sodium sulfate as the source of sulfate ions can, on the one hand, produce a salting-out effect to trigger subsequent hydrophobic association of polymers, and on the other hand, avoid introducing additional alkaline earth metal ions into the system. This operation, combined with the phosphorus-free dispersion complexing system at the front end, blocks the formation pathway of calcium sulfate crystallization precipitation under high salt conditions.

[0021] Preferably, in step S5, the effective dosage of hydrophobic modified polyacrylamide in the aqueous phase is controlled at 3-5 mg / L, and the hydrophobic modified polyacrylamide is copolymerized from the water-soluble monomer acrylamide and the hydrophobic monomer dodecyl methacrylate.

[0022] By adopting the above technical solution, dodecyl methacrylate with a medium carbon chain length, as a hydrophobic comonomer, can provide the hydrophobic association force required to trigger the crosslinking of the hydrophobic network while maintaining the necessary water solubility of the polymer matrix.

[0023] Preferably, the hydrophobically modified polyacrylamide is prepared in advance by the following method:

[0024] Acrylamide with a total monomer molar ratio of 97.5-98.5 mol% and dodecyl methacrylate with a total molar ratio of 1.5-2.5 mol% are mixed in an aqueous phase, wherein dodecyl methacrylate is pre-dispersed by ultrasonication in an aqueous solution containing sodium dodecyl sulfate to form a micelle solution.

[0025] The pH of the mixture was adjusted to 6.5-7.0 with sodium hydroxide solution, and high-purity nitrogen gas was bubbled through to remove oxygen. Initiator was added at 0.05-0.1% of the total monomer mass. The reaction was carried out at a constant temperature of 40-45℃ for 6-8 hours. The product was obtained after washing, drying and pulverizing. The molar ratio of sodium dodecyl sulfate to dodecyl methacrylate in the preparation process was 15-25:1. The initiator was an aqueous solution of potassium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0026] By employing the above-mentioned technical solution and leveraging the solubilizing effect of the surfactant sodium dodecyl sulfate, insoluble hydrophobic monomers are encapsulated and dispersed within micromicelles. Upon entering the free radical-initiated polymerization stage, the acrylamide monomers in the aqueous phase undergo micellar copolymerization with the hydrophobic monomers within the micromicelles. This polymerization pathway promotes the distribution of hydrophobic microblocks in a micro-aggregate state on the linear backbone of polyacrylamide, forming a macromolecular microstructure that forms the basis for the polymer's ability to respond to shear flow and self-assemble into a three-dimensional network.

[0027] Preferably, in step S5, the fluid mixing device is a Venturi-type tubular mixer, and the variable cross-section inlet is located 0.5 meters before the inlet of the contraction section; the specific implementation of the induction process is as follows: the Reynolds number of the fluid in the contraction section is controlled to be 1500-2000, and the fluid residence time is 1.0-2.0s; the Reynolds number of the fluid in the throat section is controlled to be 4500-5000, and the fluid residence time is 0.1-0.5s; the Reynolds number of the fluid in the expansion section is controlled to be 800-1000, and the fluid residence time is 2.0-4.0s.

[0028] By employing the above technical solution, the changes in fluid dynamic parameters inside the Venturi tube directly participate in the time control of the polymer's physicochemical phase transition. Specifically, the laminar stretching effect provided by the contraction section ensures the initial uniform distribution of the mixed drug solution; after the fluid enters the throat section, the abrupt change in cross-section generates high Reynolds number turbulence, and the shear force applied during the short residence time forces the hydrophobic groups to be exposed; finally, in the expansion section, the flow velocity decreases and the pressure rises, and the polymer chain segments, having escaped the high-shear environment, complete interchain hydrophobic association and network contraction in this relatively low-speed region.

[0029] Preferably, in step S3, the washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75 μm for classification, the underflow coarse sand is discharged into a dewatering screen for treatment, and the overflow product is used as a fine mud suspension; in step S6, the filter press dewatering is carried out under the condition of a feed pressure of 0.8-1.2 MPa; the thickening equipment is a deep cone thickener, whose central feed well is directly connected to the tail end of the fluid mixing equipment in step S5.

[0030] By adopting the above technical solution, the physical operating boundary of the solid-liquid separation module was established. The mud after flow field-induced mixing is directly fed into the feed well of the deep cone thickener. The gravity compression of the deep mud bed initially increases the underflow concentration. Then, in conjunction with the forced dewatering by the filter press, an operating closed loop that reduces water consumption and improves the closed-loop clean water reuse rate is constructed at the engineering level.

[0031] This invention provides an integrated process for low-water-consumption sand and gravel washing and grading. It offers the following advantages:

[0032] 1. This invention utilizes a phosphorus-free dispersing and complexing agent composed of sodium polyacrylate and sodium gluconate, added to the circulating sand washing water, to convert free calcium and magnesium ions into stable water-soluble complexes through the coordination and complexation of carboxylate ions with polyvalent alkaline earth metal ions. This technical feature effectively inhibits the precipitation of inorganic scale such as calcium carbonate and calcium sulfate in high-salt closed-loop systems without introducing exogenous phosphorus, maintaining the normal flow capacity of the system pipelines and dewatering equipment.

[0033] 2. This invention employs a combination of inorganic sulfate and hydrophobically modified polyacrylamide to treat fine mud suspensions. The strong hydration effect of high-concentration sulfate ions reduces the solubility of macromolecular polymers and creates a thermodynamic salting-out background in the local aqueous phase. This chemical conditioning process allows the hydrophobically modified polyacrylamide to overcome the configurational curling failure problem of conventional flocculants in high-salt environments. Furthermore, it utilizes the repulsive force of water molecules on nonpolar groups to induce intermolecular association, forming a three-dimensional network structure with certain mechanical strength, thereby improving the flocculation and sedimentation performance of fine mud slurry.

[0034] 3. This invention employs a Venturi-type tubular mixer with abrupt cross-sectional changes to treat the slurry after chemical dosing, causing the fluid to undergo rapid changes in shear rate and Reynolds number within the equipment. This spatial physical flow field forces the polymer molecular chains to expand, prompting them to rapidly complete hydrophobic cross-linking and macroscopic network contraction under the previously constructed salting-out background. Relying on the mechanical contraction force of this cross-linked network, capillary-bound water trapped inside the fine slurry flocs is squeezed out into the free aqueous phase, thereby reducing the moisture content of the downstream filter cake and improving the clean water reuse rate of the closed-loop system. Attached Figure Description

[0035] Figure 1 This is a comparison curve of the settling rate of fine mud flocs under different reagent systems of the present invention;

[0036] Figure 2 This is a graph showing the relationship between the flocculant dosage and the residual turbidity of the supernatant in this invention.

[0037] Figure 3 This is a graph showing the relationship between the shear rate of the variable cross-section flow field and the apparent viscosity of the slurry according to the present invention.

[0038] Figure 4 This is a graph showing the changes in storage modulus and loss modulus of the hydrophobically modified polyacrylamide associative network under salting-out conditions according to the present invention.

[0039] Figure 5 This is a diagram showing the effect of flow field induction time on the particle size distribution of fine mud flocs according to the present invention.

[0040] Figure 6 This is a comparison diagram of the bound water content inside the fine mud flocs before and after flow field induction according to the present invention;

[0041] Figure 7 This is a graph showing the variation of the moisture content of the filter cake under different filtration pressures according to the present invention.

[0042] Figure 8 This is a graph showing the relationship between the dosage of the phosphorus-free dispersing complexing agent of the present invention and the concentration of free calcium ions in the aqueous phase;

[0043] Figure 9 This is a comparison chart of the continuous operating time and the scaling rate of the circulating water system of the present invention.

[0044] Figure 10 This is a comparison chart showing the amount of fresh water consumed per ton of sand in the process of this invention and the conventional sand washing process. Detailed Implementation

[0045] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Those skilled in the art should understand that, within the scope of the technical concept of the present invention, equivalent substitutions, modifications or combinations of specific parameters or components in the embodiments are all within the scope of protection of the present invention.

[0046] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0047] Sodium polyacrylate, CAS number 9003-04-7, chemical formula (C3H3NaO2)n, is a homopolymer of repeating units with a straight-chain structure, in which the weight average molecular weight ranges from 2000 to 5000, the molecular weight distribution index ranges from 1.2 to 1.5, and it is of industrial grade.

[0048] Sodium gluconate, CAS number 527-07-1, chemical formula C6H 11 NaO7, industrial grade.

[0049] Polyaluminum ferric silicate is an inorganic composite polymer coagulant with an aluminum-iron copolymer crosslinking network structure based on a silicate skeleton. It has a basicity of 45% to 55%, an iron content of 2% to 3% by mass fraction, and an aluminum content of 9% to 11% by alumina. It is an industrial grade product.

[0050] Anhydrous sodium sulfate, CAS number 7757-82-6, chemical formula Na2SO4, purity greater than or equal to 95%, industrial grade.

[0051] Acrylamide, CAS No. 79-06-1, chemical formula C3H5NO, analytical grade.

[0052] Dodecyl methacrylate, CAS No. 142-90-5, chemical formula C16H30O2, analytical grade.

[0053] Sodium dodecyl sulfate, CAS number 151-21-3, chemical formula C 12 H 25 NaSO4, analytical grade.

[0054] Potassium persulfate, CAS number 7727-21-1, chemical formula K2S2O8, analytical grade.

[0055] Sodium bisulfite, CAS No. 7631-90-5, chemical formula NaHSO3, analytical grade.

[0056] Sodium hydroxide, CAS number 1310-73-2, chemical formula NaOH, analytical grade.

[0057] Anhydrous ethanol, CAS number 64-17-5, chemical formula C2H6O, analytical grade.

[0058] Preparation Example 1:

[0059] This preparation example provides a method for preparing hydrophobically modified polyacrylamide A, including the following steps:

[0060] S1: Deionized water is added to a reactor equipped with a mechanical stirrer, nitrogen conduit and condenser, followed by the addition of water-soluble monomer acrylamide, so that its mass concentration in the aqueous phase is 18%.

[0061] S2: Dissolve the hydrophobic monomer dodecyl methacrylate in an aqueous solution containing the surfactant sodium dodecyl sulfate, and ultrasonically disperse for 18 minutes to form a transparent micelle solution. Add the micelle solution to the above reaction vessel. The total molar ratio of the monomers is set as follows: acrylamide accounts for 98.0 mol%, dodecyl methacrylate accounts for 2.0 mol%, and the molar ratio of sodium dodecyl sulfate to dodecyl methacrylate is 20:1.

[0062] S3: Adjust the pH of the mixture to 6.8 using a 10% sodium hydroxide solution, bubble high-purity nitrogen gas to remove oxygen for 40 minutes, and keep the water bath temperature constant at 42 degrees Celsius.

[0063] S4: Add potassium persulfate and sodium bisulfite aqueous solution in a mass ratio of 1:1 to 0.08% of the total monomer mass.

[0064] S5: Seal the reactor and react at a constant temperature for 7 hours to form a transparent colloidal product. Take out the product, cut it into pieces, wash it three times with anhydrous ethanol, place it in a vacuum drying oven at 60 degrees Celsius and dry it to constant weight. Pulverize it to obtain white hydrophobic modified polyacrylamide A.

[0065] Preparation Example 2:

[0066] This preparation example provides a method for preparing hydrophobically modified polyacrylamide B, including the following steps:

[0067] S1: Add deionized water to a reactor equipped with a mechanical stirrer, nitrogen conduit and condenser, and then add water-soluble monomer acrylamide to make its mass concentration in the aqueous phase 15%.

[0068] S2: Dissolve the hydrophobic monomer dodecyl methacrylate in an aqueous solution containing the surfactant sodium dodecyl sulfate, and ultrasonically disperse for 15 minutes to form a transparent micelle solution. Add the micelle solution to the above reaction vessel. The total molar ratio of the monomers is set as follows: acrylamide accounts for 98.5 mol, dodecyl methacrylate accounts for 1.5 mol, and the molar ratio of sodium dodecyl sulfate to dodecyl methacrylate is 15:1.

[0069] S3: Adjust the pH of the mixture to 6.5 with a 10% sodium hydroxide solution, bubble high-purity nitrogen gas to remove oxygen for 30 minutes, and keep the water bath temperature constant at 40 degrees Celsius.

[0070] S4: Add potassium persulfate and sodium bisulfite aqueous solution in a mass ratio of 1:1 to each other at 0.05% of the total monomer mass.

[0071] S5: Seal the reactor and react at a constant temperature for 6 hours to form a transparent colloidal product. Take out the product, cut it into pieces, wash it twice with anhydrous ethanol, place it in a vacuum drying oven at 60 degrees Celsius and dry it to constant weight. Pulverize it to obtain white hydrophobic modified polyacrylamide B.

[0072] Preparation Example 3:

[0073] This preparation example provides a method for preparing hydrophobically modified polyacrylamide C, including the following steps:

[0074] S1: Add deionized water to a reactor equipped with a mechanical stirrer, nitrogen conduit and condenser, and then add water-soluble monomer acrylamide to make its mass concentration in the aqueous phase 20%.

[0075] S2: Dissolve the hydrophobic monomer dodecyl methacrylate in an aqueous solution containing the surfactant sodium dodecyl sulfate, and ultrasonically disperse for 20 minutes to form a transparent micelle solution. Add the micelle solution to the above reaction vessel. The total molar ratio of the monomers is set as follows: acrylamide accounts for 97.5 mol, dodecyl methacrylate accounts for 2.5 mol, and the molar ratio of sodium dodecyl sulfate to dodecyl methacrylate is 25:1.

[0076] S3: Adjust the pH of the mixture to 7.0 with a 10% sodium hydroxide solution, bubble high-purity nitrogen gas to remove oxygen for 45 minutes, and keep the water bath temperature constant at 45 degrees Celsius.

[0077] S4: Add potassium persulfate and sodium bisulfite aqueous solution in a mass ratio of 1:1 to 0.1% of the total monomer mass.

[0078] S5: Seal the reactor and react at a constant temperature for 8 hours to form a transparent colloidal product. Take out the product, cut it into pieces, wash it three times with anhydrous ethanol, place it in a vacuum drying oven at 60 degrees Celsius and dry it to constant weight. Pulverize it to obtain white hydrophobic modified polyacrylamide C.

[0079] Example 1:

[0080] This embodiment provides an integrated process for low-water-consumption sand and gravel washing and grading, including the following steps:

[0081] S1: Start the closed-loop circulation system for sand washing water, and control the clean water supply valve through the online conductivity monitor to keep the total dissolved solids in the circulating return water stable at 3500mg / L and the conductivity maintained at 5800uS / cm.

[0082] S2: The muddy sand and gravel raw material is continuously fed into the spiral sand washer, and the circulating return water from step S1 is pumped in, controlling the liquid-solid mass ratio in the sand washer to be 0.6:1. A phosphorus-free dispersing and complexing agent composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:2 is continuously metered and added at the feed inlet, controlling the total effective mass concentration of this phosphorus-free dispersing and complexing agent in the sand washing aqueous phase to be 100 mg / L. The pH value of the mixed slurry system is maintained at 8.8 by adding a 5% sodium hydroxide solution.

[0083] S3: The washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75um for classification. The underflow coarse sand enters the dewatering screen for treatment, and the overflow fine mud suspension enters the fine mud treatment pipeline.

[0084] S4: Inject 20 mg / L of polyaluminum ferric silicate into the fine mud suspension to construct an inorganic micro-flocculation framework; then add anhydrous sodium sulfate to the system and control the amount added so that the mass concentration increase of sulfate ions in the local aqueous phase reaches 250 mg / L, thereby constructing a local high-concentration salting-out background.

[0085] S5: Pump the fine mud suspension into a Venturi-type tubular mixer connected to the central feed well of the deep cone thickener. Inject a 0.1% (w / w) solution of hydrophobic modified polyacrylamide A obtained in Preparation Example 1 at a position 0.5 meters before the inlet of the converging section of the mixer, with the effective dosage controlled at 4 mg / L. Control the Reynolds number of the fluid in the converging section of the Venturi-type mixer to be 1800 and the fluid residence time to be 1.5 s; control the Reynolds number of the fluid in the throat section to be 4800 and the fluid residence time to be 0.3 s; control the Reynolds number of the fluid in the expanding section to be 900 and the fluid residence time to be 3.0 s.

[0086] S6: The slurry treated by the mixer is discharged into the deep cone thickener for gravity settling. The underflow slurry from the thickener is pumped into the filter press by a high-pressure slurry pump, where it is dewatered and discharged under a feed pressure of 1.0 MPa. The overflow water from the thickener and the filtrate from the filter press are collected in the clear water tank and returned to step S1 for recycling.

[0087] Example 2:

[0088] This embodiment provides an integrated process for low-water-consumption sand and gravel washing and grading, including the following steps:

[0089] S1: Start the closed-loop circulation system for sand washing water, and control the clean water supply valve through the online conductivity monitor to keep the total dissolved solids in the circulating return water stable at 3000 mg / L and the conductivity maintained at 5000 uS / cm.

[0090] S2: The muddy sand and gravel raw material is continuously fed into the spiral sand washer at a constant rate. The circulating return water from step S1 is pumped in, and the liquid-to-solid mass ratio in the sand washer is controlled at 0.5:1. A phosphorus-free dispersing complexing agent composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:1.5 is continuously metered and added at the feed inlet, and the total effective mass concentration of the phosphorus-free dispersing complexing agent in the sand washing water phase is controlled at 80 mg / L. The pH value of the mixed slurry system is maintained at 8.5 by adding a 5% sodium hydroxide solution.

[0091] S3: The washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75um for classification. The underflow coarse sand enters the dewatering screen for treatment, and the overflow fine mud suspension enters the fine mud treatment pipeline.

[0092] S4: Inject 25 mg / L of polyaluminum ferric silicate into the fine mud suspension to construct an inorganic micro-flocculation framework; then add anhydrous sodium sulfate to the system and control the dosage to make the mass concentration increase of sulfate ions in the local aqueous phase reach 300 mg / L, thereby constructing a local high-concentration salting-out background.

[0093] S5: Pump the fine mud suspension into a Venturi-type tubular mixer connected to the central feed well of the deep cone thickener. Inject a 0.1% (w / w) solution of hydrophobic modified polyacrylamide B obtained in Preparation Example 2 at a depth of 0.5 meters before the inlet of the converging section of the mixer, with the effective dosage controlled at 3 mg / L. Control the Reynolds number of the fluid in the converging section of the Venturi-type mixer to be 1500 and the fluid residence time to be 1.0 s; control the Reynolds number of the fluid in the throat section to be 4500 and the fluid residence time to be 0.1 s; control the Reynolds number of the fluid in the expanding section to be 800 and the fluid residence time to be 2.0 s.

[0094] S6: The slurry treated by the mixer is discharged into the deep cone thickener for gravity settling. The underflow slurry from the thickener is pumped into the filter press by a high-pressure slurry pump, where it is dewatered and discharged under a feed pressure of 0.8 MPa. The overflow water from the thickener and the filtrate from the filter press are collected in the clear water tank and returned to step S1 for recycling.

[0095] Example 3:

[0096] This embodiment provides an integrated process for low-water-consumption sand and gravel washing and grading, including the following steps:

[0097] S1: Start the closed-loop circulation system for sand washing water, and control the clean water supply valve through the online conductivity monitor to keep the total dissolved solids in the circulating return water stable at 4000 mg / L and the conductivity maintained at 6500 uS / cm.

[0098] S2: The muddy sand and gravel raw material is continuously fed into the spiral sand washer, and the circulating return water from step S1 is pumped in, controlling the liquid-solid mass ratio in the sand washer to be 0.8:1. A phosphorus-free dispersing complexing agent composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:2.5 is continuously metered and added at the feed inlet, controlling the total effective mass concentration of this phosphorus-free dispersing complexing agent in the sand washing aqueous phase to be 120 mg / L. The pH value of the mixed slurry system is maintained at 9.0 by adding a 5% sodium hydroxide solution.

[0099] S3: The washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75um for classification. The underflow coarse sand enters the dewatering screen for treatment, and the overflow fine mud suspension enters the fine mud treatment pipeline.

[0100] S4: Inject 30 mg / L of polyaluminum ferric silicate into the fine mud suspension to construct an inorganic micro-flocculation framework; then add anhydrous sodium sulfate to the system and control the dosage to make the mass concentration increase of sulfate ions in the local aqueous phase reach 350 mg / L, thereby constructing a local high-concentration salting-out background.

[0101] S5: Pump the fine mud suspension into a Venturi-type tubular mixer connected to the central feed well of the deep cone thickener. Inject a 0.1% (w / w) solution of hydrophobic modified polyacrylamide C obtained in Preparation Example 3 0.5 m before the inlet of the converging section of the mixer, with the effective dosage controlled at 5 mg / L. Control the Reynolds number of the fluid in the converging section of the Venturi-type mixer to be 2000 and the fluid residence time to be 2.0 s; control the Reynolds number of the fluid in the throat section to be 5000 and the fluid residence time to be 0.5 s; control the Reynolds number of the fluid in the expanding section to be 1000 and the fluid residence time to be 4.0 s.

[0102] S6: The slurry treated by the mixer is discharged into the deep cone thickener for gravity settling. The underflow slurry from the thickener is pumped into the filter press by a high-pressure slurry pump, where it is dewatered and discharged under a feed pressure of 1.2 MPa. The overflow water from the thickener and the filtrate from the filter press are collected in the clear water tank and returned to step S1 for recycling.

[0103] Example 4:

[0104] This embodiment provides an integrated process for low-water-consumption sand and gravel washing and grading, including the following steps:

[0105] S1: Start the closed-loop circulation system for sand washing water, and control the clean water supply valve through the online conductivity monitor to keep the total dissolved solids in the circulating return water stable at 3500mg / L and the conductivity maintained at 5800uS / cm.

[0106] S2: The muddy sand and gravel raw material is continuously fed into the spiral sand washer, and the circulating return water from step S1 is pumped in, controlling the liquid-solid mass ratio in the sand washer to be 0.6:1. A phosphorus-free dispersing and complexing agent composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:2 is continuously metered and added at the feed inlet, controlling the total effective mass concentration of this phosphorus-free dispersing and complexing agent in the sand washing aqueous phase to be 100 mg / L. The pH value of the mixed slurry system is maintained at 8.8 by adding a 5% sodium hydroxide solution.

[0107] S3: The washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75um for classification. The underflow coarse sand enters the dewatering screen for treatment, and the overflow fine mud suspension enters the fine mud treatment pipeline.

[0108] S4: Inject a polyaluminum ferric silicate solution into the first dosing port at the front end of the fine sludge suspension delivery pipeline, controlling its effective dosage in the aqueous phase to be 25 mg / L. Inject a 10% sodium sulfate solution into the second dosing port, controlling the sodium sulfate dosage to ensure that the local increase in the mass concentration of sulfate ions in the aqueous phase reaches 300 mg / L.

[0109] S5: Pump the fine mud suspension into a Venturi-type tubular mixer connected to the central feed well of the deep cone thickener. Inject a 0.1% (w / w) solution of hydrophobic modified polyacrylamide A obtained in Preparation Example 1 at a position 0.5 meters before the inlet of the converging section of the mixer, with the effective dosage controlled at 4 mg / L. Control the Reynolds number of the fluid in the converging section of the Venturi-type mixer to 1600 and the fluid residence time to 1.2 s; control the Reynolds number of the fluid in the throat section to 4600 and the fluid residence time to 0.2 s; and control the Reynolds number of the fluid in the expanding section to 950 and the fluid residence time to 3.5 s.

[0110] S6: The slurry treated by the mixer is discharged into the deep cone thickener for gravity settling. The underflow slurry from the thickener is pumped into the filter press by a high-pressure slurry pump, where it is dewatered and discharged under a feed pressure of 1.0 MPa. The overflow water from the thickener and the filtrate from the filter press are collected in the clear water tank and returned to step S1 for recycling.

[0111] Comparative Example 1:

[0112] Compared with Example 1, the differences are as follows: in step S1, the system is a low TDS clean water circulation (without forced control of the circulating return water TDS balance); in step S2, no phosphorus-free dispersing complexing agent composed of sodium polyacrylate and sodium gluconate is added; in step S4, no sodium sulfate solution is injected; in step S5, a straight pipe mixer of equal diameter (with the Reynolds number maintained at 2000 throughout the process) is used instead of a Venturi-type tubular mixer, and an equal amount of conventional industrial-grade anionic polyacrylamide is added instead of hydrophobic modified polyacrylamide A, and the rest are the same.

[0113] Comparative Example 2:

[0114] Compared with Example 1, the differences are: in step S1, the system uses low TDS clean water circulation; in step S4, the second dosing port is removed, that is, sodium sulfate solution is not injected to create a high salt background, and the rest are the same.

[0115] Comparative Example 3:

[0116] Compared with Example 1, the difference is that in step S5, the Venturi-type tubular mixer is replaced with a conventional high-shear tubular static mixer, so that the Reynolds number of the fluid is kept constant at 4800 throughout the entire mixing process (the fluid dynamic gradient change space is missing), and the rest are the same.

[0117] Comparative Example 4:

[0118] Compared with Example 1, the difference is that in step S5, the injected hydrophobically modified polyacrylamide A solution is replaced with a conventional industrial-grade anionic polyacrylamide solution with the same mass concentration, volume and similar molecular weight (without dodecyl hydrophobic side chains on the polymer chain), while the rest are the same.

[0119] Comparative Example 5:

[0120] Compared with Example 1, the difference is that in step S2, the phosphorus-free dispersing complexing agent composed of sodium polyacrylate and sodium gluconate added to the feed port is replaced with sodium hexametaphosphate with an equal total effective mass concentration; in step S4, the sodium sulfate solution injected into the second dosing port is replaced with magnesium sulfate solution with an equal molar concentration, and the rest are the same.

[0121] Test Example 1:

[0122] The effectiveness of the phosphorus-free chelate dispersion system in the solid-liquid stripping stage was confirmed by quantitative analysis of the existing forms of multivalent metal ions in the aqueous phase and the charge balance state on the surface of solid particles.

[0123] Experimental steps:

[0124] 1. The overflow slurry sample from step S2 of the sand washing process was used as the test mother liquor. It was centrifuged at 12000 r / min for 20 min using a high-speed centrifuge, filtered through a 0.45 μm filter membrane, and the free Ca in the original aqueous phase was measured. 2+ and Mg 2+ The initial mass concentration was measured to be at an extremely high level of initial hardness background.

[0125] 2. According to the proportions described in Examples 1 to 4, prepare phosphorus-free dispersing complexing agents containing sodium polyacrylate and SG respectively, and add equal amounts of each component of the examples into a stirred reactor containing 2L of raw ore suspension (solid content of 5%), and stir at a constant temperature for 15min at a speed of 200r / min.

[0126] 3. A separate control group was set up, in which control group 1 was not given any drug, and control group 2 was given sodium hexametaphosphate (SHMP) at the same effective mass concentration, as a reference for comparative example 5.

[0127] 4. After the reaction is complete, centrifuge again and collect the supernatant. Inductively coupled plasma optical emission spectrometry (ICP-OES) is used to determine the remaining free Ca in the filtrate. 2+ and Mg 2+ Mass concentration was used to calculate the masking rate of different reagent systems for multivalent cations.

[0128] 5. Using a Zeta potential analyzer, each group of suspensions after the reaction was diluted to a mass concentration of 0.1%, and the Zeta potential on the surface of clay particles was measured multiple times within a pH range of 8.5 to 9.0. The average value of 5 measurements was taken as the final charge characterization result.

[0129] 6. Observe and count the natural sedimentation volume of each group of samples after standing for 10 minutes, and record the turbidity change of the supernatant to evaluate the macroscopic effect of interparticle repulsion on dispersion stability.

[0130] Experimental data:

[0131] Table 1: Summary Table of Chelation Masking Effect and Interface Potential Test Data

[0132]

[0133] Based on the data in Table 1 and Figure 1 and Figure 2The test curves clearly demonstrate the excellent performance of the phosphorus-free dispersion system proposed in this invention in treating high-hardness circulating water. In Examples 1 to 4, after the addition of the reagent, the free Ca in the aqueous phase... 2+ and Mg 2+ The concentration dropped sharply, and the masking rate remained stable above 91%, confirming the strong chelating ability of sodium gluconate (SG) in the pH 8.5-9.0 environment. The polyhydroxy and carboxyl groups in the SG molecule work synergistically to form stable five- or six-membered chelate rings, successfully locking the multivalent cations that would otherwise cause particle aggregation into a complex state from the edge of the electric double layer, effectively eliminating the negative interference of cations on charge neutralization.

[0134] Regarding interfacial charge regulation, the absolute value of the Zeta potential after treatment in each embodiment significantly increased from the original -11.2 mV to the range of -38 mV to -45 mV. This significant negative shift in potential is mainly attributed to the synergistic effect of sodium polyacrylate and SG. After the long-chain structure of sodium polyacrylate is adsorbed onto the clay surface, the high-density carboxyl groups released by its dissociation not only significantly increase the negative charge density of the surface but also prevent kinetic collisions between particles through the steric hindrance effect of the polymer chain. In contrast, although the treatment effect of Comparative Example 5 was better than that of the blank group, its Zeta potential was only maintained at -28.6 mV, and the turbidity of the supernatant was still relatively high, indicating that the anti-interference ability of traditional phosphate is significantly insufficient in dealing with the background of high-salinity circulating water.

[0135] A key technical phenomenon was observed in the experiment: in Example 3, at the highest reagent ratio, the Zeta potential reached an extreme value of -45.1 mV. This indicates that by optimizing the mass ratio of sodium polyacrylate to SG, near-perfect spontaneous exfoliation of extremely fine clay particles can be achieved. This electrical regulation provides ideal preconditions for the intervention of PAFS in subsequent steps, ensuring that the clay particles are in a highly dispersed and stable state, thereby guaranteeing that the inorganic coagulant can target and neutralize the dispersed particles. Overall, this test confirms that the proposed scheme successfully reconstructs the solid-liquid interface environment through chemical means, achieving efficient mud and sand desorption at low liquid-solid ratios, laying a thermodynamic foundation for the low water consumption operation of the entire process.

[0136] Test Example 2:

[0137] By measuring the viscosity abrupt change during shear rheology and the thermodynamic enthalpy change of water in different forms inside the flocs, the feasibility of hydrophobic association and network water squeezing mechanism is confirmed from a physicochemical perspective.

[0138] Experimental steps:

[0139] 1. Extract the fine mud suspensions from Examples 1 to 4 and Comparative Examples 2, 3, and 4 that have completed inorganic coagulation and salting-out background reconstruction (i.e., completed step S4) as the base sample mother liquor for rheological and thermodynamic testing.

[0140] 2. Using a rotational rheometer with a coaxial cylindrical testing system, polymer solutions were synchronously injected into each group of mother liquors under a constant temperature of 25.0 degrees Celsius. A step shear rate scan was preset in the rheometer program to simulate the flow field changes inside the Venturi tube, causing the shear rate to jump abruptly from 50 s^-1 at the bottom to 5500 s^-1 in the simulated throat section within 0.1 s. The critical shear rate at which the apparent viscosity of the system dropped sharply and the final apparent viscosity after the shear field was unloaded were recorded.

[0141] 3. Extract the flocculated sediment generated after the flow field treatment in step S5 of the complete simulation, and determine the water content in the sediment using differential scanning calorimetry (DSC). Accurately weigh approximately 12.5 mg of wet sediment sample and seal it in an aluminum standard crucible, then introduce high-purity nitrogen as a protective gas.

[0142] 4. In a differential scanning calorimeter, the sample was cooled to -45°C at a rate of 10°C / min and held at this temperature for 5 minutes to allow the free water to crystallize completely. Then, the temperature was uniformly increased to 25°C at the same rate. The endothermic peak of the ice melting process was recorded. The enthalpy change of the freezeable free water was calculated by integrating the peak area. The free water content was calculated by comparing this value with the standard enthalpy of melting of pure water (334 J / g). After further subtraction, the mass fraction of bound water that is difficult to remove from the flocs was obtained.

[0143] Experimental data:

[0144] Table 2: Fluid Dynamics Phase Transition and Thermodynamic Test Data of Water Speciation Inside Flocs

[0145]

[0146] Based on the data in Table 2 and Figure 3 and Figure 4The example groups all exhibited significant rheological abrupt changes under the high-shear flow field of the simulated throat section. When the shear rate reached above 4500 s^-1, the apparent viscosity of the system dropped sharply and remained at an extremely low level of around 15 mPa·s. Based on the enthalpy of fusion data from thermodynamic tests, the bound water content inside the flocs generated in the example groups was significantly compressed to below 10%. In routine engineering separation practices, it has been found that conventional polymeric flocculants often lose their flocculation and bridging ability in high-salt environments due to electrostatic shielding causing random coiling of molecular chains. The data from Comparative Example 4 is consistent with this phenomenon. Since the added material was conventional anionic polyacrylamide without hydrophobic side chains, the system exhibited high viscosity and a bound water content as high as 26.8% even under extremely low shear force, proving that it completely failed in high-salt systems. The mechanism of this invention lies in the introduction of hydrophobically modified polyacrylamide and the supplementation with a high-concentration sulfate background. The extremely strong shear stress overcomes the coiling entropy within the polymer chain, forcing the chain segments to stretch. The exposed dodecyl hydrophobic side chains spontaneously associate instantaneously to escape the repulsion of the high-saltwater phase. Comparative Example 2, lacking the sulfate salting-out background, experienced the same flow field, but its phase transition driving force was insufficient, resulting in a persistently high final viscosity and the bound water content remaining at the traditional level of 28.1%. The spatial gradient of the flow field is also a necessary condition for the establishment of this mechanism. In Comparative Example 3, the system was always in a state of constant diameter and high shear. Due to the lack of a low-shear relaxation environment provided by the expansion section, the hydrophobic crosslinking network could not produce an isotropic volume shrinkage effect. Some inorganic floc skeletons were destroyed by excessive shear force, causing the tiny particles to re-encapsulate water molecules, causing its bound water content to rebound to 19.4%. Cross-validation of rheological and thermodynamic physical data confirms that the specific chemical reagent ratios and customized Venturi tube fluid dynamics parameters in this process form an inseparable interlocking relationship. Relying on this specific spatiotemporal coupling effect, the capillary water-holding structure inside the traditional flocs is successfully destroyed, and the deep water squeezing process of converting interstitial bound water into free water phase is completed.

[0147] Test Example 3:

[0148] The overall process scheme is evaluated for its separation effect on fine mud suspension by using macroscopic engineering indicators. The focus is on examining the overflow water quality after thickening and settling, as well as the final dewatering depth in the filter press stage, thereby quantitatively verifying the technical advantages of this invention in achieving extremely low water holding capacity flocs.

[0149] Experimental steps:

[0150] 1. The instantaneous slurry after processing by the mixer in step S5 in Examples 1 to 4 and Comparative Examples 1 to 4 was selected as the experimental object. Each group of samples was injected into a 1L graduated cylinder for natural sedimentation experiment. The sedimentation displacement of the solid-liquid interface in the first 5 minutes was observed and recorded to evaluate the initial formation rate of flocs.

[0151] 2. After the suspension in the graduated cylinder has settled for 30 minutes, collect the supernatant at a depth of 5 cm from the liquid surface using a pipette, and determine the suspended solids concentration (SS) using gravimetric analysis. Specifically, weigh a 0.45 μm microporous membrane that has been pre-dried to constant weight, filter 100 mL of the supernatant, and then dry the membrane containing the retained material in a 105°C oven to constant weight. Calculate the mass of suspended solids per unit volume.

[0152] 3. Collect the dense slurry at the bottom of the sedimentation chamber and conduct dewatering filtration tests using an experimental chamber filter press. Pump the slurry into the filter chamber, maintain the feed pressure at 1.0 MPa, and maintain the filtration time for 15 minutes until no continuous water drips from the outlet.

[0153] 4. Remove the filter cake after pressing, take multiple samples at the center and edges of the filter cake and mix them evenly. Accurately weigh about 20g of the wet filter cake and place it into an evaporating dish of known mass.

[0154] 5. Place the evaporating dish in a constant temperature drying oven at 105 degrees Celsius and bake until the mass difference between the two weighings is less than 0.01g. Calculate the moisture content of the mud cake based on the mass loss before and after drying.

[0155] Experimental data:

[0156] Table 3: Summary Table of Sludge-Water Separation Efficiency and Dewatering Performance Test Data

[0157]

[0158] Based on the data in Table 3 and Figure 5 and Figure 6 Comparative analysis shows that the low-water-consumption treatment process constructed in this invention exhibits significant performance advantages in actual dewatering efficiency, with the moisture content of the sludge cake consistently controlled between 38% and 42%. In contrast, the conventional process (Comparative Example 1) and the process that simply replaced the reagent (Comparative Example 4) both had sludge cake moisture contents exceeding 65%, accompanied by severe overflow and turbidity. This performance difference directly confirms the unique phase transition behavior of hydrophobically modified polyacrylamide under high salt precipitation conditions. When strong structural ions such as sulfate are present in the system, after the hydrophobically modified polyacrylamide undergoes high shear stretching through the Venturi throat, its exposed side chains undergo intense hydrophobic association. The resulting cross-linked network generates a strong inward contraction force at the moment of shear unloading. This physical compression forces the water that was originally tightly bound in the clay pores to be expelled.

[0159] Observation of the data in Comparative Example 2 reveals that although the settling velocity is acceptable, the moisture content of the sludge cake is still as high as 59.2%. This indicates that in the absence of the salting-out thermodynamic potential energy constructed by sodium sulfate, the hydrophobic groups of the hydrophobic modified polyacrylamide cannot overcome the solvation effect of the aqueous phase to achieve sufficient association, resulting in the retention of a large number of capillary water-holding structures inside the flocs. Further analysis of the results of Comparative Example 3 shows that if the gradient change of the Venturi flow field is missing, the continuous high shear environment will irreversibly destroy the micro-flocculated inorganic skeleton constructed by PAFS, causing the overflow water SS to rise sharply to 642.1 mg / L. This indicates that this process is not a simple agent stacking, but rather achieves spatiotemporal synergy of first protecting the skeleton, then stretching the chain segments, and finally extruding and shrinking through the coupling of fluid dynamic gradient and chemical background.

[0160] In long-term circulating water simulations, the mud cake generated in the example group was dry and hard, with a dry cross-section and did not stick to the filter cloth. This improvement in macroscopic physical properties is of great significance for reducing the labor intensity in industrial settings. Comprehensive experimental observations show that this solution, through precise control of the thermodynamic state of the solid-liquid interface, not only solves the problem of difficult sedimentation of fine mud but also fundamentally eliminates the high water-holding effect of fine mud. This high-clarity overflow and high-dryness mud cake achieved with extremely low water consumption provides practical technical support for the sand and gravel washing industry to achieve true closed-loop circulation and efficient water resource utilization.

[0161] Test Example 4:

[0162] By monitoring the fresh water replenishment and the evolution trajectory of total dissolved solids (TDS) in the circulating water during different operating cycles, we can assess whether the process can achieve a physical closed loop of salinity with extremely low water consumption and maintain the effectiveness of the reagents in high-salt environments.

[0163] Experimental steps:

[0164] 1. Establish a pilot-scale closed-loop water circuit test platform including a spiral sand washer, hydrocyclone, high-frequency dewatering screen, venturi tubular mixer, deep cone thickener and chamber filter press. Using the process parameters set in Examples 1 to 4 and Comparative Example 1 as the operating benchmark, continuously feed natural sand and gravel ore with an initial mud content of 18%.

[0165] 2. The system is designed to process 5 tons of raw ore per water circulation cycle, and to run continuously for 50 complete batches. During each batch, the amount of fresh deionized water required to maintain a constant total system volume is recorded via a clean water supply valve and an online level monitoring device. The average water consumption per ton of ore for each group is calculated based on the total processing capacity.

[0166] 3. At the nodes where the pilot-scale platform is continuously running until the end of the 1st, 10th, 20th, 30th, 40th and 50th batch cycles, 500 mL of recycled water samples are extracted from the clear water tanks that collect the overflow water from the thickener and the filtrate.

[0167] 4. The conductivity of the water sample was measured at 25 degrees Celsius using a high-precision benchtop conductivity meter (with temperature compensation function), and converted into the total dissolved solids (TDS) mass concentration in the aqueous phase according to the instrument’s built-in nonlinear conversion coefficient.

[0168] 5. Summarize the actual water consumption during the entire operation cycle and the TDS concentration test results at each node, and compare and analyze the salt accumulation rate of the system under the limiting liquid-solid ratio and its final equilibrium state.

[0169] Experimental data:

[0170] Table 4: Test Data on Water Consumption and TDS Evolution of Circulating Water During Continuous System Operation

[0171]

[0172] Based on the data in Table 4 and Figure 7 and Figure 8 This process achieves extremely low fresh water consumption and dynamic closed-loop system materials during actual continuous operation. In traditional sand washing operations, to prevent dispersant failure and subsequent flocculation deterioration due to salt accumulation in the suspended system, it is often necessary to rely on large amounts of fresh water for forced dilution, accompanied by discharge. This situation is clearly reflected in the data of Comparative Example 1, where the fresh water consumption per ton of sand is as high as 1.65 m³. 3 Although the low TDS level of about 500 mg / L was maintained by a large amount of clean water replacement, this treatment model, which comes at the cost of excessive water consumption, greatly increases environmental protection and operating costs.

[0173] In Examples 1 to 4, under the set low liquid-to-solid ratio conditions, the fresh water consumption was significantly reduced to an extremely low range of 0.12 to 0.18 m³ / t. This extremely low water consumption is attributed to the precise targeting of multivalent ions by the front-end phosphorus-free masking agent, fundamentally eliminating the system's dependence on low-hardness pure water. During long-term operation monitoring, it was observed that the TDS of the circulating return water in the examples rapidly increased in the initial operation stage with the continuous input of raw ore leaching salt and process reagents. When the system operated stably for 30 to 40 batches, the salt enrichment curve in the aqueous phase showed a clear inflection point of slowing growth, eventually reaching a flat plateau. This dynamic equilibrium was established following a strict law of conservation of mass. The sludge cake discharged from the filter press and the wet finished sand discharged from the dewatering screen, while removing water from the system, also proportionally stripped away the dissolved salts. When the rate of salt excretion completely offsets the amount of salt added to the system with each batch, the TDS of the macroscopic system no longer experienced disordered enrichment.

[0174] A deeper technical connection lies in the fact that the stable high TDS (3000-4000 mg / L) background maintained in the examples precisely matches the design intent of this invention to construct a strongly promoting structural environment through sulfate ions. The high concentration of coexisting salts did not trigger the salt shrinkage failure reaction of conventional polymeric flocculants; instead, it significantly enhanced the repulsive force of the hydration layer on the nonpolar side chains of the hydrophobically modified polyacrylamide, providing a stable and abundant thermodynamic driving force for the subsequent hydrophobic network water-squeezing mechanism in the Venturi flow field. The process design naturally constructs the required chemical reaction potential energy through physical equilibrium laws, transforming what was originally considered a burdensome salt accumulation into an endogenous driving force for maintaining efficient dehydration of the system. This demonstrates that this closed-loop water washing scheme possesses excellent long-term stability and industrial applicability without the need for external desalination equipment.

[0175] Test Example 5:

[0176] The difference between the phosphorus-free chelating system of this invention and the conventional phosphate system in preventing calcium and magnesium scale deposition was quantitatively evaluated by static plating method, confirming the engineering reliability of this process in long-term continuous production.

[0177] Experimental steps:

[0178] 1. Extract the reflux water from Example 1 after 50 consecutive batches of test example 4 (representing the phosphorus-free / sodium sulfate system of the present invention), and the reflux water from simulated comparative example 5 at the same concentration factor (representing the sodium hexametaphosphate / magnesium sulfate system, with its initial TDS controlled at around 3500 mg / L).

[0179] 2. The two types of high-salinity circulating water were injected into two constant-temperature water baths with a volume of 10L, respectively, and the water temperature was maintained at 35 degrees Celsius, which is common in actual production. The water was then stirred in an internal micro-circulation at a flow rate of 0.5m / s to simulate the hydrodynamic conditions in industrial pipelines.

[0180] 3. Select standard corrosion and scaling test plates made of Q235 carbon steel (size 50mm×25mm×2mm), polish their surfaces to a mirror finish with sandpaper of progressively increasing grit, ultrasonically clean and degrease them with anhydrous ethanol, and then dry them in a desiccator for 24 hours. Use an analytical balance to accurately weigh the initial mass of each plate.

[0181] 4. The pretreated carbon steel plates were suspended and immersed in two water bath circulation tanks respectively, and the continuous immersion test time was set to 720 hours (30 days). During this period, a set of plates was removed from the tank every 120 hours.

[0182] 5. After removing the pads, allow them to air dry at room temperature. Measure the apparent thickness of the scale layer using calipers, then weigh the entire pad, including the attached scale layer. Calculate the scaling weight gain per unit area (mg / cm²) based on the mass difference before and after weighing and the pads' surface area. 2 ).

[0183] 6. Take scale samples from the surface of the pads of the five comparative groups at the 720-hour mark, grind them into powder, and use X-ray diffraction (XRD) to perform rapid qualitative scanning of the phase composition of the scale layer to identify the chemical composition of the main scaling substances.

[0184] Experimental data:

[0185] Table 5: Test Data on Scaling and Weight Gain of Static Coated Plates on Pipe Walls of Circulating Water Systems

[0186]

[0187] Based on the data in Table 5 and Figure 9 and Figure 10 The process of this invention demonstrates a decisive advantage in preventing equipment scaling. In Example 1, during a high-salt immersion test lasting 720 hours, the scaling weight gain rate of the carbon steel pads was extremely low and the increase was very gradual, ultimately reaching only 0.19 mg / cm³. 2 The surface of the plate still maintains a good metallic base color and flatness. In industrial applications, it contains high concentrations of polyvalent cations (such as Ca). 2+ Mg 2+Circulating water systems often face a severe risk of inorganic salt deposition. Example 1 uses a phosphorus-free dispersing complexing agent composed of sodium polyacrylate (sodium polyacrylate) and sodium gluconate (SG). Utilizing the strong chelating ability of SG polyhydroxycarboxylic acid, free calcium and magnesium ions in the solution are firmly locked within soluble five- or six-membered cyclic complexes. Even with a TDS (total dissolved solids) in the aqueous phase of the circulating system as high as 3500 mg / L, this chemical masking effect remains extremely stable, fundamentally cutting off the formation pathway of insoluble calcium carbonate or calcium sulfate crystal nuclei.

[0188] In contrast, data from Comparative Example 5 showed that after replacing the phosphorus-free chelating agent with an equivalent concentration of sodium hexametaphosphate (SHMP) and introducing magnesium sulfate, the scaling and weight gain rate of the pads exhibited an exponentially worsening trend. Within the first 120 hours, the weight gain rate reached 1.85 mg / cm³. 2 The surface began to turn white; by the end of 720 hours, the weight gain rate had surged to 45.22 mg / cm³. 2 The feed plate was completely coated with a dense, hard, grayish-white scale. Subsequent XRD analysis of the scale revealed that its main components were calcium phosphate and magnesium phosphate crystals. SHMP hydrolyzes in alkaline and high-temperature (35°C) water environments, generating orthophosphate ions (PO4). 3- When these free orthophosphate ions encounter high concentrations of calcium and magnesium ions in the aqueous phase, the system rapidly breaks through thermodynamic supersaturation due to the extremely small solubility product constant (Ksp) of calcium phosphate / magnesium. This leads to heterogeneous nucleation and rapid growth of sparingly soluble inorganic salts on the pipe walls and rough metal surfaces of the equipment. In the comparative example, the artificially added magnesium sulfate, intended to create a salting-out environment, directly introduces a large amount of scale-causing target ions (Mg²⁺) into the system. 2+ This greatly accelerates the deposition process of magnesium phosphate hard scale.

[0189] The comparison of these macroscopic data confirms that the choice of sodium sulfate instead of other sulfates (such as aluminum sulfate or magnesium sulfate) in step S4, and the strict restriction on the use of phosphorus-free dispersants in step S2, are not simply due to cost considerations or arbitrary reagent substitution. This chemical system is built upon a profound understanding of the scaling kinetics of circulating water. Sodium ions in sodium sulfate, as monovalent cations, do not participate in the scaling reaction of alkaline earth metals. Simultaneously, the high concentration of sulfate ions, under a specific phosphorus-free, strongly chelating background, only provides salting-out potential energy and does not combine with calcium or magnesium ions to precipitate. A tight logical closed loop is formed between the various steps of the process, satisfying the high salting-out background required to trigger the hydrophobic polymer phase transition, while completely eliminating the scaling risks in the closed-loop system using phosphorus-free chelating agents, ensuring the long-term safe operation of the entire electromechanical equipment of the sand washing production line.

[0190] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-water-consumption integrated process for sand and gravel washing and grading, characterized in that, Includes the following steps: S1: Start the closed-loop circulation system for sand washing water and control the total dissolved solids in the circulating return water to maintain within the set range; S2: Feed the muddy sand and gravel raw material into the sand washing equipment, pump in the circulating return water, and add a phosphorus-free dispersing complexing agent to the sand washing water phase to adjust the mixed slurry system to be weakly alkaline, so as to target and mask the multivalent metal ions in the water phase and prevent the system from scaling. S3: Classify the washed and stripped slurry to separate the fine mud suspension; S4: Inorganic polymeric flocculant and inorganic sulfate are sequentially injected into the fine mud suspension to construct an inorganic micro-flocculation framework and a local high-concentration salting-out background; S5: The treated fine mud suspension is passed into a fluid mixing device with a cross-sectional abrupt change, and hydrophobic modified polyacrylamide is injected before the variable cross-section inlet. The shear rate abrupt change and spatial gradient flow field inside the fluid mixing device are used to induce hydrophobic association and generate three-dimensional network contraction in the salting-out background, forcibly squeezing out the capillary bound water inside the fine mud flocs. S6: The treated slurry is discharged into a thickening device for gravity settling, the underflow slurry is dewatered by pressure filtration, and the overflow water from the thickening device and the filtrate from the pressure filtration are returned to step S1 as circulating water.

2. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S1, the total dissolved solids in the circulating return water are controlled to be stable at 3000-4000 mg / L, and the conductivity is maintained at 5000-6500 uS / cm. In step S2, the liquid-solid mass ratio in the sand washing equipment is controlled to be (0.5-0.8):1, and the pH value of the mixed slurry system is maintained at 8.5-9.

0.

3. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S2, the phosphorus-free dispersing complexing agent is composed of sodium polyacrylate and sodium gluconate in a mass ratio of 1:(1.5-2.5), and its total effective mass concentration in the sand washing aqueous phase is controlled at 80-120 mg / L.

4. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S4, the inorganic polymeric flocculant is polyaluminum iron silicate, and its effective dosage in the aqueous phase is 20-30 mg / L; the inorganic sulfate is anhydrous sodium sulfate, and its dosage is controlled so that the mass concentration increase of sulfate ions in the local aqueous phase reaches 250-350 mg / L.

5. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S5, the effective dosage of the hydrophobic modified polyacrylamide in the aqueous phase is controlled at 3-5 mg / L, and the hydrophobic modified polyacrylamide is copolymerized from the water-soluble monomer acrylamide and the hydrophobic monomer dodecyl methacrylate.

6. The integrated low-water-consumption sand and gravel washing and grading process according to claim 5, characterized in that, The hydrophobically modified polyacrylamide was prepared in advance by the following method: Acrylamide with a total monomer molar ratio of 97.5-98.5 mol% and dodecyl methacrylate with a total molar ratio of 1.5-2.5 mol% are mixed in an aqueous phase, wherein dodecyl methacrylate is pre-dispersed by ultrasonication in an aqueous solution containing sodium dodecyl sulfate to form a micelle solution. The pH of the mixture was adjusted to 6.5-7.0 with sodium hydroxide solution, and high-purity nitrogen gas was bubbled through to remove oxygen. Initiator was added at 0.05-0.1% of the total monomer mass. The mixture was reacted at a constant temperature of 40-45℃ for 6-8 hours. The product was obtained after washing, drying and pulverizing.

7. The integrated low-water-consumption sand and gravel washing and grading process according to claim 6, characterized in that, The molar ratio of sodium dodecyl sulfate to dodecyl methacrylate in the preparation process is (15-25):1; the initiator is an aqueous solution of potassium persulfate and sodium bisulfite in a mass ratio of 1:

1.

8. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S5, the fluid mixing device is a Venturi-type tubular mixer, and the variable cross-section inlet is located 0.5 meters before the inlet of the contraction section; The specific implementation of the induction process is as follows: the Reynolds number of the fluid in the contraction section is controlled to be 1500-2000, and the fluid residence time is 1.0-2.0s; the Reynolds number of the fluid in the throat section is controlled to be 4500-5000, and the fluid residence time is 0.1-0.5s; the Reynolds number of the fluid in the expansion section is controlled to be 800-1000, and the fluid residence time is 2.0-4.0s.

9. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S3, the washed and stripped slurry is discharged into a hydrocyclone with a separation particle size of 75 μm for classification, the underflow coarse sand is discharged into a dewatering screen for treatment, and the overflow product is used as the fine mud suspension.

10. The integrated low-water-consumption sand and gravel washing and grading process according to claim 1, characterized in that, In step S6, the filter press dewatering is carried out under the condition of a feed pressure of 0.8-1.2 MPa; the thickening equipment is a deep cone thickener, whose central feed well is directly connected to the tail end of the fluid mixing equipment described in step S5.

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