Sintering machine head ash and desilication sludge solid waste diversified disposal method

Abstract

The application discloses a kind of sintering machine head ash and desilication sludge solid waste diversified disposal method, after sintering machine head ash and desilication sludge are matched with water and pre-soluble, through multistage centrifugal water washing and remove chlorine to obtain mud ash washing filtrate;Afterwards, through calcium carbonate hardening and decalcification, activated carbon powder organic matter adsorption, ultrafiltration, ammonia nitrogen stripping and carbon dioxide stripping and nanofiltration monovalent ion filtrate, high-purity potassium salt and sodium salt are obtained by crystallization and salt separation again.The application can effectively utilize the acidic components in desilication sludge by sintering machine head ash and desilication sludge cooperated water washing and remove chlorine, make the insoluble substances in sintering machine head ash dissolve, and the two are treated cooperatively, not only can realize the resource utilization of sintering machine head ash and desilication sludge, but also can obtain high-purity potassium salt and sodium salt.

Description

Technical Field

[0001] This invention relates to the field of environmental solid waste treatment technology, and more specifically, to a diversified treatment method for sintering machine head ash and desiliconization sludge solid waste. Background Technology

[0002] Sintering machine head ash (hereinafter referred to as "machine head ash") is dust and particulate matter collected by dust removal equipment (filter bags) during the smelting process in steel plants, as well as ash and sludge captured by dust collectors at the high-temperature furnace mouths of the sintering unit and ironmaking process. Sintering machine head ash is a special type of fly ash specific to the steel industry. Its solid elemental composition differs significantly from that of domestic waste sintering ash. Its main components are iron, potassium, sodium, chlorine, and a certain amount of calcium carbonate. Among these, potassium, sodium, and lead are primarily present as ferrous (Fe2+) and ferric (Fe3+) elements, while other elements commonly found in domestic fly ash are present in smaller quantities. There are three traditional methods for disposing of sintering machine head ash: first, temporary storage in a designated area and outsourced disposal, which carries the risk of secondary pollution and is costly; second, direct return to the sintering process, which easily leads to alkali metal enrichment, causing problems such as "clumpy grate bars" in sintering, thus affecting the yield and quality of sintered ore; and third, extraction of solid iron slag using leaching, but this technology has low dechlorination efficiency and low resource recovery rate, failing to achieve resource utilization of the machine head ash. Therefore, it is necessary to explore an efficient and environmentally friendly method for the resource utilization of sintering machine head ash, taking into account its characteristics.

[0003] Desilication sludge mainly originates from the acid regeneration process in steel production. It contains a large amount of harmful components such as chloride ions and ammonia nitrogen, which makes it difficult to render the sludge harmless and utilize its resources. Desilication sludge belongs to category HW17 in the National Hazardous Waste List. Its pH value is around 1 to 2 and its chloride ion content is around 13% to 18%. It cannot be used directly in steel production. The main pollutants that need to be treated are chloride ions and heavy metals such as iron.

[0004] Since the annual output of sintering machine head ash and desiliconization sludge is relatively large and has certain reuse value, this invention develops a process for the co-processing of sintering machine head ash and desiliconization sludge, based on the characteristics of these two types of waste, thus realizing the harmless treatment and resource reuse of sintering machine head ash and desiliconization sludge. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a diversified treatment method for solid waste of sintering machine head ash and desiliconization sludge. By synergistically washing and dechlorinating sintering machine head ash and desiliconization sludge with water, the acidic components in the desiliconization sludge can be effectively utilized to dissolve the insoluble substances in the sintering machine head ash. The synergistic treatment of the two not only achieves the harmless treatment and resource utilization of sintering machine head ash and desiliconization sludge, but also obtains high-purity potassium and sodium salts.

[0006] This invention provides a diversified treatment method for sintering machine head ash and desilication sludge solid waste, comprising the following steps:

[0007] S1, mix sintering machine head ash and desilication sludge at a mass ratio of 4~6:1, and pre-dissolve them in water at a liquid-solid ratio of 2~4:1 to obtain sludge-ash mixture slurry;

[0008] S2, the mud-lime mixture is subjected to multi-stage centrifugal washing and dechlorination to obtain wet slag and mud-lime washing filtrate;

[0009] S3, detect the calcium and magnesium ion content in the sludge washing filtrate, add sodium carbonate to remove hardening and decalcification, and then obtain the sludge hardening filtrate by plate and frame filter press.

[0010] S4, add activated carbon powder to the de-hardening filtrate for organic matter adsorption, stir and react, and then filter through plate and frame filter press to obtain sludge decarbonization filtrate.

[0011] S5, the sludge decarbonization filtrate is ultrafiltered through a microfiltration membrane, and then the ultrafiltered filtrate is stripped of ammonia nitrogen and carbon dioxide. After stripping, the filtrate is finely filtered through a nanofiltration membrane to remove divalent and higher ions, and the freshwater product is collected to obtain monovalent ion filtrate.

[0012] S6. The monovalent ion filtrate is evaporated and concentrated until the concentrations of sodium and potassium salts are close to the maximum precipitation eutectic saturation point. The evaporated concentrate is then transferred to a double-effect freeze crystallizer and rapidly cooled to below -5°C to directly precipitate potassium salts. The process continues until the potassium ion concentration of the remaining mother liquor after crystallization is <10wt%. The mother liquor is then transferred to a triple-effect evaporator to precipitate sodium salts through evaporation and crystallization.

[0013] Preferably, in step S1, the pre-dissolving time is 1~2 hours.

[0014] Preferably, in step S2:

[0015] The multi-stage centrifugal washing dechlorination includes at least three stages of centrifugal washing. After each stage of centrifugal washing, the filtration is performed. The filtrate after the next stage of centrifugal washing is returned to the previous stage of centrifugal washing. The liquid-solid ratio of each stage of centrifugal washing is controlled to be 3-4:1.

[0016] The chloride ion content in the washed wet residue is <1 wt%;

[0017] In the mud ash water-washing filtrate, the chloride ion content is ≥30wt%.

[0018] Preferably, in step S3:

[0019] The detection of calcium ion and magnesium ion contents adopts inductively coupled plasma optical emission spectrometry;

[0020] The dosage of sodium carbonate is added at a mass ratio of calcium carbonate to sodium carbonate of 1:1 to 1.2 after converting the calcium ion and magnesium ion contents in the mud ash water-washing filtrate into calcium carbonate content.

[0021] Preferably, in step S4, the dosage of the activated carbon powder is added according to the TOC content in the hard-removed filtrate. After converting the TOC content into CODcr at a ratio of 1:3, at least 1 kg of activated carbon powder is used for every 200 mg of CODcr, and the stirring reaction time is >1 h.

[0022] Preferably, in step S5, the ammonia nitrogen stripping and carbon dioxide stripping processes are carried out in a stripping tower; during ammonia nitrogen stripping, sodium hydroxide is first used to adjust the pH of the filtrate to above 10.5, then the circulating pump and blower supporting the stripping tower are turned on to perform filtrate circulation and stripping, the pH of the filtrate is monitored in real time and maintained, and the ammonia nitrogen stripping is completed until the ammonia nitrogen concentration in the filtrate is <50 mg / L; during carbon dioxide stripping, hydrochloric acid is used to adjust the pH of the filtrate to 4 to 5, the circulating pump and blower supporting the stripping tower are turned on for stripping, and the pH of the filtrate is monitored in real time, and the carbon dioxide stripping is completed until the pH of the filtrate is >6.

[0023] Preferably, in step S6, the purity of the potassium salt is ≥91%; the purity of the sodium salt is ≥95%.

[0024] The diversified disposal method for sintering machine head ash and desiliconization sludge solid waste provided by the present invention has the following beneficial effects:

[0025] 1. Compared with the single water washing of sintering machine head ash and desiliconization sludge, the cooperative water washing of sintering machine head ash and desiliconization sludge of the present invention can reduce the water distribution amount in the water washing process by using the desiliconization sludge with relatively high moisture content, reduce the final total amount of solid waste, and reduce the amount of desiliconization sludge for external disposal and the external disposal cost; in addition, the acidic compounds in the desiliconization sludge can effectively elute the insoluble solid elements in the machine head ash into the filtrate, and the acidity and alkalinity of the two can play a neutralizing role, so that no secondary pH adjustment is required during the subsequent treatment of the obtained water-wet residue and mud ash water-washing filtrate.

[0026] 2. On the one hand, the present invention reduces the chlorine-containing toxicity (below 1%) of the solid-phase water-wet residue after water washing, making it a general solid waste, and reduces the total amount of terminal solid waste for disposal; on the other hand, chlorine is washed into the filtrate, which increases the yield of salt by-products.

[0027] 3. This invention uses ammonia nitrogen stripping and carbon dioxide stripping, which can effectively remove ammonia nitrogen and carbon dioxide from the filtrate, thereby improving the quality of salt by-products from terminal crystallization and desalination, reaching or exceeding the national standard level II.

[0028] 4. This invention effectively utilizes the components of desilication sludge and sintering machine head ash, effectively mixing the two for synergistic treatment, reducing the volume of solid waste disposal; improving energy conservation in production, and realizing the recycling of solid waste resources as well as low-carbon and green environmental protection.

[0029] 5. The sludge and ash washing filtrate obtained by the desilication sludge and co-washing machine head of the present invention, after being subjected to filtrate hardening removal, ultrafiltration, filtrate ammonia nitrogen removal, carbon dioxide removal and nanofiltration, the refined filtrate, and the sodium and potassium salts obtained by crystallization and salt separation meet the quality requirements of the national second-level industrial salt standard. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process for the diversified treatment of sintering machine head ash and desiliconization sludge solid waste according to the present invention.

[0031] Figure 2 The phase diagram of the KCl-NaCl-H2O ternary aqueous salt system in the initial filtrate of this invention;

[0032] Figure 3 This is the phase diagram of the KCl-NaCl-H2O ternary aqueous salt system after potassium chloride is extracted by freeze crystallization according to the present invention. Detailed Implementation

[0033] To better understand the above-described technical solutions of the present invention, the technical solutions of the present invention are further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are merely illustrative of one aspect of the present invention and are not intended to limit the scope of the present invention. The present invention can be employed under various conditions as long as it does not depart from the spirit of the present invention and achieves its objectives.

[0034] This invention conducts detection, analysis and tracking experiments on sintering machine head ash and desilication sludge, and combines various scientific instruments to conduct multi-path data detection on experimental samples and filtrates. For example, it uses a fixed-target X-ray diffractometer of the Dutch Panaco X-Pert PRO MPD model to analyze the phase and crystal form of the samples, a constant temperature induction furnace drying oven, a Myron multiphase water quality detector, a Hach hardness meter, and a Shangyi turbidity meter. Through a large number of experiments on the co-treatment of sintering machine head ash and desilication sludge, it was found that: (1) The components of multiple indicators of sintering machine head ash and desilication sludge are basically the same, and both come from the steel casting process production section. Due to the different production purposes of the process, a suitable ratio needs to be removed during the co-treatment process; (2) The components of sintering machine head ash and desilication sludge are the same, and co-treatment can reduce the total amount of residual solid waste; (3) The potassium and sodium elements in sintering machine head ash and desilication sludge have a high proportion and can be effectively extracted. Based on the above research, this invention designs a diversified disposal method for solid waste of sintering machine head ash and desilication sludge.

[0035] Combination Figure 1 As shown, the present invention provides a diversified treatment method for sintering machine head ash and desilication sludge solid waste, comprising the following steps:

[0036] S1, mix sintering machine head ash and desilication sludge at a mass ratio of 4~6:1, and pre-dissolve them in water at a liquid-solid ratio of 2~4:1 to obtain sludge-ash mixture slurry;

[0037] This step is the pre-dissolution process. Before pre-dissolution, the composition of the sintering machine head ash and desilication sludge can be tested. The sintering machine head ash is a special fly ash in a specific steel industry. Its main components are iron, potassium, sodium, chlorine, and a certain amount of calcium carbonate. It also contains lead compounds and calcium compounds that are only found in high-chlorine and high-salt environments. The desilication sludge belongs to category HW17 in the National Hazardous Waste List. Its pH value is around 1 to 2, and its chloride ion content is around 13% to 18%.

[0038] In this step, sintering machine head ash and desilication sludge are mixed in a mass ratio of 4~6:1 by conveyor or screw conveyor into a premixing tank and pre-dissolved with water at a liquid-solid ratio of 2~4:1 for 1~2 hours to obtain sludge-ash mixture.

[0039] S2, the mud-lime mixture is subjected to multi-stage centrifugal washing and dechlorination to obtain wet slag and mud-lime washing filtrate;

[0040] This step is a multi-stage centrifugal washing and dechlorination process, which includes at least three stages of centrifugal washing. After each stage of centrifugal washing, the liquid is filtered, and the filtrate from the next stage of centrifugal washing is returned to the previous stage of centrifugal washing. The liquid-to-solid ratio of each stage of centrifugal washing is controlled to be 2-4:1, and each stage of centrifugal washing can last for 3-5 minutes.

[0041] In a specific implementation case, a three-stage centrifugal washing and dechlorination process is adopted. The mud-ash mixture is fed into the centrifugal washing system. The mud-ash mixture is first pumped into the first-stage centrifuge for primary centrifugal washing. The filtrate after washing is sent to the washing filtrate tank for later use as mud-ash washing filtrate. The solid phase from the primary centrifugal washing enters the primary sludge tank, and water is added at a liquid-to-solid ratio of 2-4:1. After being mixed evenly, it is pumped into the secondary centrifuge for secondary centrifugal washing. The secondary filtrate after washing flows back to the primary centrifuge. The solid phase from the first-stage centrifugal washing and second-stage centrifugal washing enters the second-stage sludge tank, where water is added at a liquid-to-solid ratio of 2–4:1. After thorough mixing, the solid phase is pumped into the third-stage centrifugal washing unit. The filtrate from the third-stage centrifugal washing is then returned to the second-stage centrifugal washing unit for further washing. After drying, the solid phase from the third-stage centrifugal washing unit is tested. If the chloride ion content is less than 1 wt%, it can proceed to the remaining solid phase treatment process for co-processing with other solid phases generated subsequently. Otherwise, it is returned to the pre-dissolution process.

[0042] The sludge filtrate obtained after multi-stage centrifugal washing and dechlorination has a chloride ion content of ≥30wt%, such as 32.3wt%.

[0043] In the pre-dissolution process of step S1 and the multi-stage centrifugal washing and dechlorination process of step S2, it is necessary to mix the sintering machine head ash and desiliconization sludge for co-washing. The reason is that if the sintering machine head ash and desiliconization sludge are washed separately, the resulting filtrate has certain limitations in actual processes. For example, the sintering machine head ash has a high absolute solids content, reaching over 93%, resulting in a large water consumption during water mixing. At the same time, some metal elements are sparingly soluble and cannot be dissolved in water during single washing (such as calcium sulfate, calcium carbonate, and phosphate). (e.g., tricalcium, etc.); desilication sludge has a high concentration of chloride ions, and the content of other metal elements except iron is trace. After the two are washed together, on the one hand, the water supply can be reduced, and on the other hand, the acidic compounds in the desilication sludge can effectively wash away the insoluble solid elements in the machine head ash into the filtrate. Compared with washing alone, the concentration of calcium, magnesium and other ions in the filtrate increases to a certain extent, and the acidity and alkalinity of the two can play a neutralizing role. Therefore, there is no need to adjust the pH again when treating the wet sludge and sludge filtrate in subsequent washing.

[0044] S3, detect the calcium and magnesium ion content in the sludge washing filtrate, add sodium carbonate to remove hardening and decalcification, and then obtain the sludge hardening filtrate by plate and frame filter press.

[0045] This step is the decalcification process, where calcium and magnesium ion content is detected using inductively coupled plasma atomic emission spectrometry (ICP-AES). Sodium carbonate is then added for decalcification, following the reaction: CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl. After stirring, the solid phase (CaCO3) is removed by plate and frame filtration, yielding a sludge decalcification filtrate. The amount of sodium carbonate used is calculated as follows: the calcium and magnesium ion concentrations are measured using ICP-AES, and these are converted to the total calcium carbonate concentration. Then, the amount of sodium carbonate is calculated based on a calcium carbonate to sodium carbonate mass ratio of 1:1~1.2.

[0046] S4, add activated carbon powder to the de-hardening filtrate for organic matter adsorption, stir and react, and then filter through plate and frame filter press to obtain sludge decarbonization filtrate.

[0047] This step is the carbon adsorption process. To ensure the subsequent extraction of sodium and potassium salts as byproducts and the protection of the membrane system in water treatment, and because the TOC content of the desiliconized sludge is high, the total organic carbon in the hardening filtrate needs to be degraded and removed. The amount of activated carbon powder is added according to the TOC content in the hardening filtrate. After converting the TOC content to CODcr at a ratio of 1:3, at least 1 kg of activated carbon powder is used for adsorption for every 200 mg CODcr. Therefore, it is necessary to test the total amount of organic matter in the hardening filtrate. After adding activated carbon powder, the reaction is stirred for more than one hour (e.g., 1-2 hours). After stirring, the activated carbon solids are removed by plate and frame filter press to obtain the sludge decarbonized filtrate.

[0048] The wet sludge washed by multi-stage centrifugation and dechlorination in step S2, the de-hardening and decalcification solid phase after plate and frame filtration in step S3, and the activated carbon solid phase after plate and frame filtration in step S4 can be co-processed in the remaining solid phase treatment process and then treated as general solid waste.

[0049] S5, the sludge decarbonization filtrate is ultrafiltered through a microfiltration membrane, and then the ultrafiltered filtrate is stripped of ammonia nitrogen and carbon dioxide. After stripping, the filtrate is finely filtered through a nanofiltration membrane to remove divalent and higher ions, and the freshwater product is collected to obtain monovalent ion filtrate.

[0050] This step involves ultrafiltration, stripping, and nanofiltration treatment of the sludge decarbonization filtrate. First, the sludge decarbonization filtrate is transported to an ultrafiltration membrane module for ultrafiltration, removing most of the residual suspended solids (SS). Then, ammonia nitrogen and carbon dioxide in the filtrate need to be stripped. Ammonia nitrogen stripping effectively reduces the presence of ammonium chloride in high-salinity water environments, preventing the disruption of the ternary aqueous salt system, thereby removing the coating of impurity salt crystals during the crystallization process and reducing the impact of impurity salts. Carbon dioxide stripping ensures stable operation of the water treatment membrane system. Furthermore, depending on the process requirements, ammonia nitrogen stripping needs to be carried out under alkaline conditions, while carbon dioxide stripping needs to be carried out under acid washing conditions.

[0051] In the specific scheme, the ammonia nitrogen stripping and carbon dioxide stripping processes are carried out in the stripping tower. During ammonia nitrogen stripping, the pH value of the filtrate is first measured, and sodium hydroxide is used to adjust the pH of the filtrate to above 10.5. Then, the circulation pump and blower of the stripping tower are turned on to circulate and strip the filtrate. The pH of the filtrate is monitored in real time (measured every 30±5 minutes) and maintained (sodium hydroxide can be added if the pH drops) until the ammonia nitrogen concentration in the filtrate is <50mg / L, at which point the ammonia nitrogen stripping is completed. During carbon dioxide stripping, hydrochloric acid is used to adjust the pH of the filtrate to 4-5, so that the proportion of free carbon dioxide in the filtrate exceeds 90%. Then, the circulation pump and blower of the stripping tower are turned on to strip the filtrate, and the pH of the filtrate is monitored in real time until the pH of the filtrate is >6, at which point the carbon dioxide stripping is completed.

[0052] After ammonia nitrogen stripping and carbon dioxide stripping are completed, the stripped filtrate is sent to a nanofiltration membrane module for nanofiltration. The filtrate is selectively filtered through the nanofiltration membrane to remove divalent and higher-valent metal ions. The permeate from the freshwater side of the nanofiltration membrane module is collected to obtain monovalent ion filtrate.

[0053] S6. The monovalent ion filtrate is evaporated and concentrated in a first-effect evaporator until the concentrations of sodium and potassium salts are close to the maximum precipitation eutectic saturation point. The concentrated evaporation solution is then transferred to a second-effect cryogenic crystallizer and rapidly cooled to a low temperature below -5°C to directly precipitate potassium salts. The potassium salt content in the remaining mother liquor after crystallization is <10wt%, and it is then fed into a third-effect evaporator to precipitate sodium salts through evaporation and crystallization.

[0054] This step is the crystallization and salt separation process. After the sintering machine head ash and desilication sludge are combined, the filtrate containing monovalent ions is tested and it is found that the potassium ion content in the filtrate is higher than that of sodium ions. Therefore, in the ternary aqueous salt system, when the solubility of potassium chloride is close to the crystallization point, the low-temperature precipitation effect of potassium salt will be achieved faster than that of sodium salt.

[0055] Based on the characteristics of the ternary aqueous salt system, when the concentration of potassium ions is higher than that of sodium ions, potassium salts in the ternary aqueous salt system will preferentially crystallize in the low-temperature region. In a freezing environment below 0°C, water will preferentially form ice crystals. A three-phase coexistence point of ice-KCl-NaCl exists in the ternary phase diagram. However, the formation of ice consumes a large number of water molecules, further increasing the relative concentration of potassium chloride in the remaining solution, greatly enhancing its supersaturation capacity and causing a large amount to precipitate. Simultaneously, the effective concentration of sodium chloride in the ternary aqueous salt system will be greatly reduced, forming a thermodynamic inhibition on sodium salt crystallization. Figure 2As shown, in the KCl-NaCl-H2O ternary aqueous salt system, after the monovalent ion filtrate is evaporated and concentrated to near saturation, and then cooled at low temperature to precipitate potassium chloride (KCl), sodium chloride (NaCl) usually does not crystallize. The core mechanism is the difference in solubility temperature dependence. The theory is that the solubility of potassium chloride (KCl) decreases significantly with decreasing temperature (the temperature coefficient is positive), with a solubility of approximately 34 g / 100g water at 20℃, and dropping to approximately 28 g / 100g water at 0℃; while the solubility of sodium chloride (NaCl) is minimally affected by temperature, remaining at 36 g / 100g water at 20℃ and still as high as 35.7 g / 100g water at 0℃. Figure 3 As shown, the blue area represents the concentration range of potassium chloride after low-temperature freezing and crystallization, and the red area represents the concentration range of sodium chloride; the black area represents the standard crystallization curve. As water evaporates, the sodium chloride region corresponding to the red area exceeds the standard crystallization curve of the black area, while the potassium chloride region corresponding to the blue area has not reached the crystallization concentration. Therefore, during the cooling process, KCl preferentially precipitates due to rapid accumulation of supersaturation, while NaCl, due to its slight change in solubility, is difficult to achieve effective supersaturation. This allows for the effective precipitation of potassium salts at low temperatures, while sodium salts remain as solutes in the aqueous solution without crystallization. By continuously adding the low-temperature residual mother liquor to the monovalent ion filtrate, the concentration of sodium ions in the subsequent monovalent ion filtrate can be effectively increased, thereby effectively widening the concentration difference between the two.

[0056] Based on the above analysis, in this step, the monovalent ion filtrate is evaporated and concentrated. The excess water in the ternary aqueous salt system is evaporated in a first-effect evaporator. After the concentrations of sodium salt and potassium salt are close to the highest precipitation eutectic saturation point, the evaporated concentrate is transferred to a second-effect cryogenic crystallizer. The concentrate is rapidly cooled to below -5°C, and potassium salt is directly precipitated at low temperature in the second-effect cryogenic crystallizer.

[0057] After potassium salt crystallization, the low-temperature residual mother liquor is stored in a triple-effect evaporator for later use, while simultaneously replenishing the feed liquid after the completion of the second-effect cryogenic crystallizer. Through the replenishment of feed liquid from the second-effect cryogenic crystallizer, the sodium ion concentration in the triple-effect evaporator gradually increases. After the second-effect cryogenic crystallization, the potassium ion concentration in the low-temperature residual mother liquor in the triple-effect evaporator is less than 10 wt%. At this point, the difference in the concentration ratio of sodium ions to potassium ions in the low-temperature residual mother liquor of this ternary water-salt system is significant. An evaporation crystallization process is then used to separate the sodium salt crystals from the triple-effect evaporator.

[0058] After the triple-effect evaporator completes sodium salt crystallization, the remaining evaporation mother liquor will enter the evaporation residue tank and be transported to the first-effect evaporator by the mother liquor return pump. It will be mixed with the newly entered first-effect evaporator in a certain proportion to increase the concentration of the original liquid, which is beneficial for providing the feed liquid concentration for the second-effect freeze crystallizer and the triple-effect evaporator.

[0059] In this step, by first precipitating potassium salt at low temperature and then precipitating sodium salt at high temperature, the purity of the obtained potassium salt is ≥91% and the purity of the sodium salt is ≥95%.

[0060] Example

[0061] The solid composition of the sintering machine head ash in this embodiment is shown in Table 1, and the solid composition of the desilication sludge is shown in Table 2.

[0062] Table 1 Solid composition of sintering machine head ash

[0063] Table 2 Solid composition of desiliconized sludge

[0064] The diversified treatment method for sintering machine head ash and desiliconization sludge solid waste in this embodiment is as follows:

[0065] (1) The sintering machine head ash and desiliconized sludge are mixed in a premixing tank at a mass ratio of 5:1, and water is added for pre-dissolution at a liquid-solid ratio of 3:1. After stirring for 1 hour, a mud-ash mixture is obtained, which is then fed into a centrifugal washing system for three-stage centrifugal washing and dechlorination.

[0066] (2) The mud-lime mixture is pumped into a primary centrifuge for primary centrifugal washing. The filtrate after washing enters the washing filtrate tank. The solid phase from the primary centrifugal washing enters the primary sludge tank. Water is added at a liquid-to-solid ratio of 3:1. After mixing evenly, the mixture is pumped into a secondary centrifuge for secondary centrifugal washing. The secondary filtrate after washing flows back to the primary centrifuge for primary centrifugal washing. The solid phase from the secondary centrifugal washing enters the secondary sludge tank. Water is added again at a liquid-to-solid ratio of 3:1. After mixing evenly, the mixture is pumped into a tertiary centrifuge for tertiary centrifugal washing. The tertiary filtrate after washing flows back to the secondary centrifuge for secondary centrifugal washing. After the tertiary centrifugal washing wet sludge is dried, if the chloride ion content is <1wt%, it enters the remaining solid phase treatment process and is disposed of in conjunction with other solid phases generated subsequently. Otherwise, it is returned to the pre-dissolution process. The chloride ion content of the mud-lime washing filtrate obtained after the above tertiary centrifugal washing dechlorination is 32.3wt%.

[0067] (3) The sludge washing filtrate in the water washing tank is transported to the decalcification tank. The calcium and magnesium ion contents are detected by inductively coupled plasma atomic emission spectrometry. The calcium ion concentration is about 4470 mg / L and the magnesium ion concentration is about 760 mg / L. The total amount of sludge washing filtrate is 30 kg. The mass ratio of calcium and magnesium ions (converted to calcium carbonate) to sodium carbonate is 1:1.059. The amount of sodium carbonate added is 455.63 g. After stirring and reacting, the solid phase (i.e. CaCO3) is removed by plate and frame filter press to obtain sludge decalcification filtrate.

[0068] Total hardness (calculated as CaCO3, mg / L) = ≈430.25g, corresponding sodium carbonate dosage = ≈455.63g;

[0069] (4) The de-hardening filtrate is fed into the carbon powder reaction tank for TOC removal. Activated carbon powder is added to adsorb the organic matter in the filtrate. The TOC concentration in the filtrate is measured to be about 638 mg / L. Activated carbon powder is added according to the principle that 1 kg of activated carbon removes 0.2 kg of CDOcr. The weight of the filtrate is calculated as 30 kg. The total TOC in the de-hardening filtrate is 19410 mg, and 97050 mg of activated carbon powder needs to be added. After stirring for more than one hour, the filtrate is filtered through a plate and frame filter press to remove the activated carbon solids that adsorbed TOC, and the sludge decarbonization filtrate is obtained.

[0070] (5) The filtrate from the decarbonization of mud ash is transported to an ultrafiltration membrane module for ultrafiltration to remove most of the residual suspended solids (SS). The filtrate passing through the ultrafiltration membrane module is then transported to a stripping tower for ammonia and carbon dioxide stripping. During ammonia stripping, the initial pH of the filtrate is first measured, and the difference is adjusted according to the POH value. Sodium hydroxide is used to adjust the filtrate to approximately 11.5, with an ammonia nitrogen concentration of approximately 480 mg / L. The circulation pump and blower of the stripping tower are then started to circulate and strip the filtrate. pH and ammonia nitrogen are measured every 30 minutes to monitor whether the pH value in the filtrate decreases during the ammonia nitrogen stripping process. Sodium hydroxide is added as needed. The pH of the filtrate was maintained at around 11.5. When the ammonia nitrogen concentration was less than 50 mg / L, ammonia nitrogen stripping was completed, and the pH of the filtrate was 7.44. Then, carbon dioxide stripping was performed. Hydrochloric acid was used to adjust the pH of the filtrate to around 5, so that the proportion of free carbon dioxide in the water exceeded 90%. Carbon dioxide stripping was carried out by circulating pump and blower, and the pH of the filtrate was monitored in real time. Stripping was completed when the pH reached 6.34. The stripped filtrate was then transported to a nanofiltration membrane module for nanofiltration. The filtrate was selectively filtered through the nanofiltration membrane to remove divalent and higher-valent metal ions. The permeate from the freshwater side of the nanofiltration membrane module was collected to obtain monovalent ion filtrate.

[0071] (6) The 15kg monovalent ion filtrate was tested, and the proportion of potassium chloride was approximately 5.08% and the proportion of sodium chloride was approximately 4.68%. The solubility characteristics of NaCl-H2O-KCl in the ternary aqueous salt system of the process system, along with temperature control, were used for effective salt separation. The monovalent ion filtrate was transported to a first-effect evaporator and concentrated until the concentrations of sodium and potassium salts were close to the maximum precipitation eutectic saturation point. Then, it was transported to a second-effect cryogenic crystallizer for cooling and crystallization. Potassium chloride crystals precipitated in the low-temperature zone of -5℃, while sodium chloride existed in ionic form in the remaining mother liquor at low temperature. The potassium salt content in the mother liquor was <10wt%, and it was then transferred to a third-effect evaporator for later use. Simultaneously, the feed liquid from the second-effect cryogenic crystallizer was replenished. Through the replenishment of the feed liquid from the second-effect cryogenic crystallizer, the sodium ion concentration in the third-effect evaporator gradually increased. At this point, the difference in the proportions of sodium and potassium ions in the feed liquid of this ternary aqueous salt system was significant. An evaporation crystallization process was used, and the temperature was raised to >60℃ to separate the sodium chloride crystals from the third-effect evaporator.

[0072] In this embodiment, 0.76 kg of potassium chloride crystals and 0.7 kg of sodium chloride crystals were obtained. The purity of the potassium chloride crystals reached 91.18%, and the specific composition is shown in Table 3, meeting the Class II standard for wet salt of "Industrial Potassium Chloride". The purity of the sodium chloride crystals reached 95.2%, and the specific composition is shown in Table 4, meeting the Class II standard for wet salt of "Industrial Sodium Chloride".

[0073] Table 3. Composition of potassium chloride crystals

[0074] Table 4. Composition of Sodium Chloride Crystals

[0075] In summary, this embodiment employs the diversified solid waste treatment method for sintering machine head ash and desilication sludge of the present invention. By co-washing and dechlorinating the sintering machine head ash and desilication sludge with water, the acidic components in the desilication sludge can be effectively utilized to dissolve the insoluble substances in the sintering machine head ash. The synergistic treatment of the two reduces the chlorine toxicity of the solid waste after washing, thereby reducing the total amount of terminal solid waste to be disposed of. On the other hand, it increases the yield of salt by-products. Through the circulation and stripping of the filtrate, ammonia nitrogen and carbon dioxide in the filtrate can be effectively removed, improving the quality of the terminal salt products and making them meet or exceed the national standard level II. Therefore, by co-treating the sintering machine head ash and desilication sludge, not only can the resource utilization of sintering machine head ash and desilication sludge be realized, but also high-purity potassium and sodium salts can be obtained.

[0076] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A diversified treatment method for sintering machine head ash and desiliconization sludge solid waste, characterized in that: comprising the following steps: In S1, sintering machine head ash and desiliconization sludge are mixed at a mass ratio of 4~6:1, and water is added for pre-dissolution at a liquid-solid ratio of 2~4:1 to obtain a sludge-ash mixed slurry; In S2, the sludge-ash mixed slurry is subjected to multi-stage centrifugal water washing for dechlorination, so as to obtain water-washed wet residue and sludge-ash water-washing filtrate; In S3, the contents of calcium ions and magnesium ions in the sludge-ash water-washing filtrate are detected, sodium carbonate is added for hardness removal and calcium removal, and then filter pressing is performed through a plate and frame filter to obtain a sludge-ash hardness-removed filtrate; In S4, activated carbon powder is added into the hardness-removed filtrate for organic matter adsorption, and after the stirring reaction, filter pressing is performed through a plate and frame filter to obtain a sludge-ash decarburized filtrate; In S5, the sludge-ash decarburized filtrate is subjected to ultrafiltration through a microfiltration membrane, then the ultrafiltered filtrate is subjected to ammonia nitrogen stripping and carbon dioxide stripping, after stripping is completed, the filtrate is subjected to fine filtration through a nanofiltration membrane to remove ions with a valence of two or more, and the produced water on the fresh water side is collected to obtain a monovalent ion filtrate; In S6, the monovalent ion filtrate is evaporated and concentrated in a first-effect evaporator, after the concentrations of sodium salt and potassium salt approach the highest precipitation eutectic saturation point, the evaporated concentrated solution is transferred to a second-effect freezing crystallizer for rapid cooling to a low temperature below -5°C to directly precipitate the potassium salt, after the potassium salt content in the low-temperature residual mother liquor after crystallization is less than 10wt%, the low-temperature residual mother liquor enters a third-effect evaporator to precipitate the sodium salt through evaporative crystallization.

2. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S1, the pre-dissolution time is 1~2h.

3. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S2: The multi-stage centrifugal water washing for dechlorination at least comprises three stages of centrifugal water washing, filtration is carried out after each stage of centrifugal water washing, the filtrate after the subsequent stage of centrifugal water washing flows back to the previous stage of centrifugal water washing process, and the liquid-solid ratio of each stage of centrifugal water washing is controlled to be 2~4:1; In the water-washed wet residue, the chloride ion content is less than 1wt%; In the sludge-ash water-washing filtrate, the chloride ion content is greater than or equal to 30wt%.

4. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S3: The detection of the calcium ion and magnesium ion contents adopts inductively coupled plasma optical emission spectrometry; The dosage of the sodium carbonate is added at a mass ratio of calcium carbonate to sodium carbonate of 1:1~1.2 after converting the calcium ion and magnesium ion in the sludge-ash water-washing filtrate into the calcium carbonate content.

5. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S4, the dosage of the activated carbon powder is added according to the TOC content in the hardness-removed filtrate, the TOC content is converted into CODcr at a ratio of 1:3, and then at least 1kg of activated carbon powder is used per 200mg of CODcr, with the stirring reaction time being more than 1h.

6. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S5, the ammonia nitrogen stripping and carbon dioxide stripping processes are carried out in a stripping tower; during ammonia nitrogen stripping, sodium hydroxide is first used to adjust the pH of the filtrate to above 10.5, then the circulating pump and blower matched with the stripping tower are turned on for filtrate circulation and stripping, the pH of the filtrate is monitored in real time and maintained, and the ammonia nitrogen stripping is completed when the ammonia nitrogen concentration in the filtrate is less than 50mg / L; during carbon dioxide stripping, hydrochloric acid is used to adjust the pH of the filtrate to 4~5, the circulating pump and blower matched with the stripping tower are turned on for stripping, and the pH of the filtrate is monitored in real time, and the carbon dioxide stripping is completed when the pH of the filtrate is greater than 6.

7. The diversified treatment method for sintering machine head ash and desilication sludge solid waste according to claim 1, characterized in that: In step S6, the purity of the potassium salt is greater than or equal to 91%; the purity of the sodium salt is greater than or equal to 95%.

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