Gold smelting wastewater desalting zero-discharge process

Abstract

The invention belongs to the technical field of gold smelting wastewater treatment, and particularly discloses a gold smelting wastewater desalting zero discharge process which comprises the following steps: S1, gold smelting wastewater is collected in an adjusting tank, enters a hardness removal reaction tank to remove hardness ions, enters a thickener to separate out supernate, and the pH of the supernate is adjusted in a pH callback tank; s2, removing suspended matters from the supernatant with the adjusted pH value through a security filter, further removing hardness through a deep softening device, and enabling the supernatant with the hardness removed to enter an evaporation raw water tank; s3, pumping wastewater in the evaporation raw water tank into an MVR evaporation system; s4, the concentrated solution in the evaporation tank enters a centrifugal machine to separate mother liquor and crystals, and the crystals enter a boiling fluidized bed dryer to be dried and then are packaged into finished salt by a full-automatic packaging machine; s5, enabling part of the mother liquor to flow back to the evaporation tank, enabling the rest to enter a scraper evaporator for evaporation and crystallization, and separating into evaporation produced water and carnallite; therefore, the wastewater is converted into evaporation produced water and finished salt, and the target value of zero discharge of the wastewater is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of gold smelting wastewater treatment, and in particular to a gold smelting wastewater desalination and zero-discharge process. Background Art

[0002] Gold smelting wastewater has always been a difficult problem in the field of water treatment due to its complex composition, containing a variety of heavy metal ions and harmful substances. Although traditional treatment methods, such as chemical precipitation, coagulation sedimentation, ion exchange and membrane filtration, can remove some pollutants in wastewater to a certain extent, they often have many disadvantages.

[0003] Chemical precipitation usually requires the addition of a large amount of chemical agents, which not only increases the treatment cost, but may also cause secondary pollution, such as excessive sediment and incompletely reacted chemicals. The coagulation and sedimentation method is easily affected by water quality fluctuations and the treatment effect is unstable. The ion exchange method is easy to saturate during the treatment process, requiring frequent resin replacement, and a large amount of waste liquid is generated during the regeneration process. The membrane filtration method has problems such as membrane pollution, membrane clogging and limited membrane life. At the same time, the high investment and operating costs also limit its wide application.

[0004] Zero discharge and resource utilization have become important goals of gold smelting wastewater treatment. Enterprises should not only achieve harmless treatment of wastewater, but also recycle useful resources in wastewater as much as possible to reduce the impact on the environment.

[0005] However, it is difficult for existing traditional treatment methods to simultaneously meet the requirements of zero discharge and resource utilization. Therefore, there is an urgent need for a simple and efficient zero discharge process for gold smelting wastewater, which can not only effectively remove harmful substances in wastewater, but also realize resource recycling and utilization, so as to achieve true green, environmental protection and sustainable development. The present invention is proposed to solve this problem and provide an innovative zero discharge process for gold smelting wastewater desalination to meet the development needs of enterprises. Summary of the invention

[0006] The purpose of the present invention is to provide a zero-discharge process for desalting gold smelting wastewater to solve the problems of poor effect, generation of secondary wastewater and high cost of single treatment technology in previous treatment processes, to achieve zero discharge of saline wastewater and to recover the salt resources in the wastewater.

[0007] To achieve the above object, the present invention provides the following technical solution, a gold smelting wastewater desalination and zero-discharge process, comprising the following steps:

[0008] S1. Gold smelting wastewater is collected in the regulating tank, enters the hardness removal reaction tank to remove hardness ions, and then enters the thickener to separate the supernatant. The pH of the supernatant is adjusted in the pH adjustment tank.

[0009] S2. After adjusting the pH, the supernatant passes through a safety filter to remove suspended solids, and then passes through a deep softening device to further remove hardness. The supernatant after hardness removal enters the evaporation raw water pool.

[0010] S3. The wastewater in the evaporation raw water pool is pumped into the MVR evaporation system. Specifically, the wastewater passes through the steam preheater and then exchanges heat with steam before entering the evaporation tank. The wastewater is forced into the heat exchanger by the circulation pump in the evaporation tank. The steam in the evaporation tank is pressurized and heated by the steam compressor before entering the heat exchanger. The steam transfers heat to the wastewater in the heat exchanger before entering the steam preheater. Finally, the steam is condensed into evaporated water and discharged.

[0011] S4. The concentrated liquid in the evaporation tank enters the centrifuge to separate the mother liquor and crystals. The crystals enter the boiling fluidized bed dryer for drying and are packaged into finished salt by the fully automatic packaging machine.

[0012] S5. Part of the mother liquor flows back to the evaporation tank, and the rest enters the scraper evaporator for evaporation and crystallization, and is separated into evaporated water and miscellaneous salts.

[0013] As a preferred embodiment of the present invention, the retention time of the regulating tank in S1 is not less than 12 hours, and a central guide tube and a mud pump are provided.

[0014] As a preferred embodiment of the present invention, the de-hardening agent in S1 is a mixture of sodium carbonate and sodium hydroxide, and the dosage is not less than 1.15 times of the total hardness; the dosage is measured by sodium ion concentration, and the total hardness is measured by calcium ion concentration.

[0015] As a preferred embodiment of the present invention, the acid used for adjusting the pH in S1 is sulfuric acid, and the pH after adjustment is between 6.5 and 7.5.

[0016] As a preferred embodiment of the present invention, the accuracy of the security filter in S2 does not exceed 20 μm, and the deep softening device is an ion exchange resin.

[0017] As a preferred embodiment of the present invention, the temperature of the steam preheater in S3 is not lower than 65°C, the temperature of the evaporator is not lower than 85°C, and the temperature of the heat exchanger is not lower than 101°C.

[0018] As a preferred embodiment of the present invention, the centrifuge in S4 has a heating evaporation function, and the evaporation crystallization function is realized during the centrifugation process.

[0019] As a preferred embodiment of the present invention, the film thickness of the scraper evaporator in S5 does not exceed 1.0 mm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention realizes the steps of wastewater pretreatment, deep softening, evaporation crystallization, drying and packaging, and separation of impurities salt through a regulating tank, a hardness removal reaction tank, a thickener, a pH adjustment tank, a security filter, a deep softening device, an MVR evaporation system, a centrifuge, a boiling fluidized bed dryer, a full-automatic packaging machine, and a scraper evaporator, and finally converts wastewater into evaporation water and finished salt, achieving the goal of zero wastewater discharge. This process not only solves the problem of gold smelting wastewater treatment, but also realizes the effective recovery and utilization of resources, and has high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0023] Figure 2 It is a schematic diagram of the implementation process of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "vertical", "up", "down", "horizontal", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0026] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] See also Figure 1 , the present invention provides a technical solution:

[0028] Step 1: The gold smelting wastewater is collected in the regulating tank, enters the hardness removal reaction tank to remove hardness ions, and then enters the thickener to separate the supernatant. The pH of the supernatant is adjusted in the pH adjustment tank.

[0029] The retention time in the regulating tank shall not be less than 12 hours, and it shall be equipped with a central guide tube and a sludge pump.

[0030] The hardness remover is a mixture of sodium carbonate and sodium hydroxide, and the dosage (sodium ion concentration meter) is not less than 1.15 times the total hardness (calcium ion concentration meter).

[0031] The acid used for adjusting the pH is sulfuric acid, and the pH after adjustment is between 6.5-7.5.

[0032] Step 2: After adjusting the pH, the supernatant is filtered through a safety filter to remove suspended solids, and then further softened by a deep softening device. The de-hardened supernatant enters the evaporation raw water pool.

[0033] The accuracy of the security filter does not exceed 20μm, and the deep softening device is ion exchange resin.

[0034] Step three, the wastewater in the evaporation raw water pool is pumped into the MVR evaporation system. Specifically, the wastewater enters the evaporation tank after heat exchange with steam through the steam preheater. The wastewater is forced into the heat exchanger by the circulation pump in the evaporation tank. The steam in the evaporation tank is pressurized and heated by the steam compressor and enters the heat exchanger. The steam transfers heat to the wastewater in the heat exchanger and enters the steam preheater. Finally, the steam is condensed into evaporated water and discharged.

[0035] The steam preheater temperature shall not be lower than 65°C, the evaporator temperature shall not be lower than 85°C, and the heat exchanger temperature shall not be lower than 101°C.

[0036] Step 4: The concentrated liquid in the evaporation tank enters the centrifuge to separate the mother liquor and crystals. The crystals enter the boiling fluidized bed dryer for drying and are packaged into finished salt by a fully automatic packaging machine.

[0037] The centrifuge has a heating evaporation function, which realizes evaporation and crystallization during the centrifugal process.

[0038] Step 5: Part of the mother liquor is returned to the evaporation tank, and the rest enters the scraper evaporator for evaporation and crystallization, and is separated into evaporation water and miscellaneous salts.

[0039] The film thickness of the scraper evaporator shall not exceed 1.0 mm.

[0040] The specific implementation method of the gold smelting wastewater desalination and zero-discharge process in the gold smelting plant wastewater treatment of the present invention is as follows:

[0041] The treated water is divided into four sources: cyanide wastewater, denitrification wastewater, refining wastewater and acidic wastewater. According to the characteristics of each water quality and quantity, the following process route analysis is carried out.

[0042] When desalting cyanide wastewater, cyanide wastewater: 11m3 / h, denitrification wastewater, 4m3 / h, refining wastewater 10~15m3 / d.

[0043] When desalting acidic wastewater, acidic wastewater: 11m3 / h, denitrification wastewater, 4m3 / h, refining wastewater 10~15m3 / d.

[0044] The cyanide-containing raw water has high contents of Ca2+, Mg2+ and Zn2+, with Ca2+ reaching 791 mg / L, Mg2+ reaching 74.3 mg / L and Zn2+: 198.1 mg / L. After mixing with 2# denitrification wastewater, the carbonate in the denitrification wastewater reacts with the Ca2+ in the cyanide-containing water to form calcium carbonate. The ion product of calcium carbonate reaches (0.87×10–8). According to theoretical calculations, the carbonate ions in the water are excessive after mixing, and they need to be neutralized to form sodium sulfate to avoid the formation of sodium glauber's salt complex salt after the sodium carbonate concentration multiples increase, which affects the stability of the system.

[0045] First, the primary decalcification reaction tank removes Mg and Zn from the cyanide-containing wastewater by adding Na2CO3 and NaOH. The concentration product of magnesium hydroxide is 1.2×10–11, and the concentration product of zinc hydroxide is 1.8×10–14. PAC and PAM agents are added to the subsequent fourth-stage decalcification reaction tank. After precipitation by an 8m thickener, the hardness can be reduced to about 50 mg / L. Ion exchange is used in the later stage to perform deep softening treatment to ensure that the hardness of the water does not exceed 50 mg / L, so as to delay the scaling cycle of the evaporation crystallization system.

[0046] The pre-treated effluent and the neutralized wastewater contain 7.3% sodium sulfate and 1.6% sodium chloride, which are concentrated 7 times in the MVR evaporation and crystallization system (sodium chloride concentration reaches 11.3%), and solid-liquid separation is performed to obtain 1.1t / h of sodium sulfate; considering the influence of sodium chloride concentration on the quality of sodium sulfate by-product salt, as much sodium sulfate as possible is recovered to reduce the output of impure salts. When the sodium chloride concentration reaches the saturation point (NaCl: 4.7%, Na2SO4: 20%), the sodium chloride concentration is controlled to be ≤20%, and the amount of mother liquor discharged to the impure salt system per hour is about 1.2t / h, and the amount of impure salt discharged from the impure salt system is about: ~0.33t / h.

[0047] According to material balance, the incoming flow of the system is 16t / h, the designed load of the sodium sulfate MVR evaporation crystallization system is 14t / h, and the amount discharged into the impure salt system is 1.2t / h. Considering the insufficient steam heat source, a steam generator is required as a heat source in winter to reduce the operating cost of the impure salt system. Considering the fluctuation of raw water, the complexity of the water quality of the project, and the unpredictability of the impact of impure salt on the quality of by-product sodium sulfate, as well as the refined smelting water and denitrification wastewater to be treated, when the quality of by-product sodium sulfate is abnormal, the discharge volume of impure salt mother liquor is increased to buffer the water quality fluctuation and product salt quality, and the impure salt system load is increased to: 3t / h, and the above system is used to achieve "zero discharge" of wastewater and "resourceization" of waste salt.

[0048] A double-stage piston pusher centrifuge is used to separate the solid and liquid of sodium sulfate crystal salt and mixed salt crystal salt.

[0049] The dried sodium sulphate products are packaged in ton bags.

[0050] For the small amount of COD contained in the wastewater brought into the raw ore, the system is equipped with a set of impure salt mother liquor drying device to avoid COD enrichment in the evaporator after the system concentrates it to a certain multiple.

[0051] The system reserves and selects a set of defoamer adding device positions. When necessary, new defoamer can be added to the crystallization evaporation chamber to eliminate foam.

[0052] The refined water is directly pretreated separately, and heavy metals (mainly Cu) are removed by adding calcium carbide slag and Na2S for neutralization and softening. The solid-liquid separation is carried out through two-stage plate and frame filter pressing. The pretreated filtrate enters the impure salt section of the salt separation system for desalination treatment.

[0053] The treatment of acidic wastewater and cyanide-containing wastewater is carried out alternately. When the salt content in the cyanide-containing wastewater drops to 40-60g / L, the system switches to treat acidic wastewater. The device equipment configuration remains unchanged. There are no specific requirements for the sodium sulfate recovery rate and the quality of the salt product. It is only required to separate sodium sulfate from miscellaneous salts, and the water quality of the system output water meets the requirements of "Water Quality for Industrial Water Use in Urban Wastewater Recycling". After the acidic wastewater is desalinated, the desalination system enters the cleaning procedure. After the system is cleaned, the cyanide-containing wastewater is treated.

[0054] It is worth noting that the entire device is controlled by a main control button. Since the device matched with the control button is a common device and belongs to the existing mature technology, its electrical connection relationship and specific circuit structure will not be described in detail here.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A zero-discharge process for desalination of gold smelting wastewater, characterized in that: The following steps are involved: S1. Gold smelting wastewater is collected in the regulating tank, enters the hardness removal reaction tank to remove hardness ions, and then enters the thickener to separate the supernatant. The pH of the supernatant is adjusted in the pH adjustment tank; S2. After adjusting the pH, the supernatant passes through a security filter to remove suspended solids, and then passes through a deep softening device to further remove hardness. The supernatant after hardness removal enters the evaporation raw water pool; S3, the wastewater in the evaporation raw water pool is pumped into the MVR evaporation system, specifically, Wastewater passes through the steam preheater and then exchanges heat with steam before entering the evaporation tank. Wastewater is forced into the heat exchanger by a circulating pump in the evaporation tank. Steam in the evaporation tank is pressurized and heated by a steam compressor before entering the heat exchanger. Steam transfers heat to wastewater in the heat exchanger before entering the steam preheater. Finally, steam is condensed into evaporated water and discharged. S4, the concentrated liquid in the evaporation tank enters the centrifuge to separate the mother liquor and crystals, the crystals enter the boiling fluidized bed dryer for drying and are packaged into finished salt by the fully automatic packaging machine; S5. Part of the mother liquor flows back to the evaporation tank, and the rest enters the scraper evaporator for evaporation and crystallization, and is separated into evaporated water and miscellaneous salts.

2. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The retention time of the regulating tank in S1 is not less than 12 hours, and a central guide tube and a mud pump are provided.

3. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The de-hardening agent in S1 is a mixture of sodium carbonate and sodium hydroxide, and the dosage is not less than 1.15 times of the total hardness; the dosage is measured by sodium ion concentration, and the total hardness is measured by calcium ion concentration.

4. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The acid used for adjusting the pH in S1 is sulfuric acid, and the pH after adjustment is between 6.5 and 7.

5.

5. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The accuracy of the security filter in S2 does not exceed 20 μm, and the deep softening device is an ion exchange resin.

6. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: In the S3, the temperature of the steam preheater is not lower than 65°C, the temperature of the evaporator is not lower than 85°C, and the temperature of the heat exchanger is not lower than 101°C.

7. A gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The centrifuge in S4 has a heating evaporation function, and realizes the evaporation crystallization function during the centrifugation process.

8. The gold smelting wastewater desalination and zero-discharge process according to claim 1, characterized in that: The film thickness of the scraper evaporator in S5 does not exceed 1.0 mm.

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