A method for resource recovery of chromium-containing electroplating sludge

Abstract

The present invention provides a method for resource recovery of chromium-containing electroplating sludge, including the process steps of pigment preparation and metal recovery. Among them, the ceramic pigment is prepared by a solid-phase method using chromium-containing electroplating sludge and calcium-silicon substances as raw materials. The waste liquid generated during the preparation process realizes the cascade recovery of metals through the methods of adding iron powder to reduce and precipitate copper, hydrogen peroxide to oxidize and precipitate iron, and reduction and flocculation to precipitate chromium. The recovered chromium hydroxide can be returned to the raw material electroplating sludge for secondary utilization. The present invention prepares a ceramic pigment with good color rendering effect and excellent acid and alkali resistance through a simple solid-phase reaction method. Moreover, the purity of the grossularite phase Ca3Cr2(SiO4)3 is relatively high, with stable properties, acid and alkali resistance, and at the same time realizes the cascade recovery of metals. The present invention realizes the resource utilization of chromium-containing sludge, a solid hazardous waste, in the field of ceramic pigments. The process is simple, easy to control, environmentally friendly, and the raw materials are cheap and easily available, greatly reducing the production cost and having good economic and environmental benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization of solid waste in the electroplating industry, and specifically relates to a method for recycling chromium-containing electroplating sludge resources. Background Art

[0002] With the rapid development of the electroplating industry, the electroplating industry has become one of the pillar industries in China. At the same time, the amount of electroplating wastewater generated has increased sharply. Electroplating sludge is the flocculent precipitate generated in the chemical treatment process of electroplating wastewater, which has the characteristics of high water content, poor stability, easy accumulation of heavy metals, easy transfer, etc., and is very harmful. At present, the annual output of electroplating sludge exceeds 10 million tons. The composition of electroplating sludge is complex, containing various heavy metals such as Cr, Ni, Cu, Zn, Pb, Cd, etc., which is the 17th category of hazardous waste listed in the "National Hazardous Waste List" and is also a globally recognized hazardous waste. In the electroplating process, organic substances such as brighteners and surfactants are often added, which makes the composition of electroplating sludge more complex and also increases the difficulty of its treatment. At present, the treatment method of electroplating sludge is still open-air stacking, which not only pollutes the surrounding environment, but also the heavy metals in it will migrate along the path of sludge - soil - crops - human body, thus directly or indirectly endangering human health. However, at present, there is no efficient and reasonable treatment method for electroplating sludge, and how to harmlessly and resourcefully treat electroplating sludge has always been a research hotspot in related fields.

[0003] Electroplating sludge often contains a large amount of heavy metals, so metal recovery and extraction are necessary treatment methods. However, the composition of electroplating sludge is complex and there are many types, and the recovery difficulty is relatively high. Therefore, this method still needs to be explored in depth. Some studies have prepared electroplating sludge into bricks or roadbed materials, and heavy metal ions are well consolidated in the cementitious system. The method is simple and efficient, but this is a serious waste of heavy metals in electroplating sludge. Preparing electroplating sludge into high-value-added materials is a more economical and reasonable treatment method, making full use of the characteristics of sludge and specifically using the heavy metals in electroplating sludge. Chromium-containing sludge is a common type of electroplating sludge with different qualities, which contains a large amount of chromium metal and is a very good raw material for preparing chromium-based ceramic pigments.

[0004] At present, there are already methods for preparing pigments using chromium-containing sludge. For example, Patent CN 110616328 proposes a method for preparing chromite black using chromium-containing sludge, which not only realizes the cascade recovery of metals but also prepares qualified chromite black pigments. CN110055425A discloses a method for preparing iron oxide red pigments from electroplating sludge. There are also many studies on preparing pigments using pure reagents such as chromium oxide or solid wastes such as aluminum ash, as shown in Patents CN 114058195 and CN 108047763. Although a lot of research work has been done on preparing ceramic pigments using electroplating sludge at present, there is still no technical research on preparing grossular ceramic green pigments using chromium-containing sludge and simultaneously realizing metal recovery, and the acid and alkali resistance of pigments is also an important performance that needs to be explored in depth.

[0005] Therefore, on the existing basis, further research is carried out to prepare calcium chromium garnet ceramic green pigment (Ca3Cr2(SiO4)3) with good color rendering performance by using chromium-containing electroplating sludge, and metals such as copper and iron are recycled in a cascade manner to realize the high-value application of solid waste. Summary of the Invention

[0006] In view of the above technical problems, the present invention proposes a method for preparing calcium chromium garnet ceramic green pigment from chromium-containing electroplating sludge and recycling metals. Calcium and silicon substances are mixed with the sludge and roasted, and solid-phase method is used to prepare calcium chromium garnet ceramic green pigment with good performance. The waste liquid generated during the preparation process can meet the sewage discharge standard after cascade treatment and metal recovery. The preparation process is simple and efficient, without secondary pollution. At the same time, the prepared pigment has good acid and alkali resistance, and has good environmental and economic benefits.

[0007] To achieve the above object, the present invention adopts the following specific technical solutions:

[0008] A method for recycling resources from chromium-containing electroplating sludge, comprising the following steps:

[0009] (1) Ball-mill the electroplating sludge, dry the ground powder, and screen it to obtain electroplating sludge powder; weigh the electroplating sludge powder, calcium carbonate, silicon dioxide, and mineralizer according to a certain ratio, mix them evenly, calcine, and take out after cooling to room temperature to obtain solid powder 1;

[0010] (2) Pickle the powder 1 obtained in step (1) at room temperature, filter to obtain filtrate A and filter residue A, wash the filter residue A three times with deionized water until neutral, combine the washing liquid and filtrate A to obtain filtrate B, and dry the washed filter residue A to obtain calcium chromium garnet ceramic green pigment;

[0011] (3) Add iron powder to the filtrate B obtained in step (2), stir at room temperature, filter after sufficient reaction to obtain copper powder and filtrate C;

[0012] (4) Add hydrogen peroxide to the filtrate C obtained in step (3), and then adjust the pH of the system to 4-5 until no more red precipitate is formed, filter to obtain Fe(OH)3 and filtrate D;

[0013] (5) Add sodium metabisulfite to the filtrate D obtained in step (4), at the same time adjust the pH of the system to 8-9, add a flocculant, stir at room temperature until no more green precipitate is formed, filter to obtain Cr(OH)3 and waste liquid; dry the filter residue Cr(OH)3 and return it to the electroplating sludge in step (1) for reuse, and treat the remaining liquid as harmless liquid.

[0014] The drying in the present invention is not particularly limited, and conventional drying methods in the art can be used, such as oven drying and vacuum drying.

[0015] In step (1), the sieving is through a 60 - 200 mesh sieve, such as 100 mesh, 120 mesh, 180 mesh.

[0016] In step (1), the Cr content in the chromium - containing electroplating sludge is 35 - 60 wt%. The chromium - containing electroplating sludge is a flocculent precipitate generated during the chemical treatment of electroplating wastewater. Due to the plating type being chromium, the chromium content in the electroplating sludge is relatively high and exists in the form of oxides or hydroxides.

[0017] In step (1), the calcium carbonate can be replaced or mixed with biomass calcium sources such as eggshells, shells, oyster shells, etc., and its dosage is calculated as CaCO3; the mass ratio of the electroplating sludge, calcium carbonate, and silica is 16 - 30:51 - 65:15 - 20; the mineralizer is selected from one or a combination of two or more of calcium fluoride, borax, sodium fluoride, boric acid, and sodium fluorosilicate. The mineralizer accounts for 2 - 10 wt% of the total mass of the mixture (the total mass of the electroplating sludge, calcium carbonate, silica, and mineralizer), preferably 4 - 6 wt%; the calcination temperature is 850 - 1200 °C, the heating rate is 5 - 10 °C / min, such as 8 °C / min; the heat preservation time is 30 - 180 min, such as 60 min, 90 min, 120 min, 150 min.

[0018] Preferably, the mineralizer is a mixture of borax and sodium fluorosilicate, where borax accounts for 50 - 75 wt%. The inventors unexpectedly found that when the mineralizer is a mixture of borax and sodium fluorosilicate, the obtained grossular - garnet ceramic green colorant has the best acid and alkali resistance, and the Cr utilization rate in the electroplating sludge is higher. The possible reason is that the compound mineralizer can significantly improve the crystal form of the colorant, making the purity of the grossular - garnet phase (Ca3Cr2(SiO4)3) higher and reducing the impurity phase, especially the formation of chrome yellow (CaCrO4). Chrome yellow can dissolve in water and acid. Its doping in the colorant not only increases the yellowness (b*) value of the colorant but also reduces the acid and alkali resistance of the colorant. A large amount of Cr dissolves in the washing water and acid washing solution, causing waste and increasing the difficulty of subsequent recovery. Sodium fluorosilicate is easy to combine with calcium and can micro - regulate the calcium content in the solid - phase reaction, improve the balance between reactants, and reduce the formation of chrome yellow, thereby improving the color rendering and chemical stability of the colorant. The inventors also tried the compounding of borax and other fluorine - containing mineralizers, but none of them achieved the same good effect as the compounding with sodium fluorosilicate.

[0019] In step (1), a crude product of the colorant is prepared, and the preparation process is simple and efficient; the raw material calcium carbonate is also a loosening agent, which decomposes carbon dioxide at high temperature to play a role in gas stirring, ensuring that the prepared colorant is loose and preventing caking.

[0020] The acid solution described in step (2) is a mixture of low-concentration hydrochloric acid, acetic acid, and water. The concentrations of hydrochloric acid and acetic acid are 20 - 40 g / L and 30 - 50 g / L respectively, and the volume ratio of the acid solution to the mass of powder 1 is 3 - 5 mL:1 g. Acid washing and water washing can remove impurities in the pigment, making the color rendering property of the pigment better and the overall greenness value also better.

[0021] The particle size of the iron powder described in step (3) is 100 - 200 mesh. The iron powder is added in 3 - 8 batches, and after each addition, it is stirred for 15 - 40 min at a stirring speed of 150 - 300 rpm. The addition of iron powder is stopped when it is monitored that the iron powder in the system no longer dissolves.

[0022] The concentration of hydrogen peroxide described in step (4) is 30 - 40 wt%, and it is added in 3 - 5 batches. After each addition, it is manually stirred for 1 - 2 min, and the addition of hydrogen peroxide is stopped when no more bubbles are generated; the alkaline solution for adjusting the pH of the system is ammonia water with a concentration of 10 - 20 wt%.

[0023] The sodium metabisulfite described in step (5) is added in 3 - 5 batches, and the alkaline solution for adjusting the pH of the system is ammonia water with a concentration of 10 - 20 wt%. The two are added simultaneously. After each addition, it is manually stirred for 1 - 2 min, and the addition of sodium metabisulfite is stopped when no more green precipitate is generated; the flocculant is selected from one or a combination of two or more of chitosan, hydroxymethyl chitosan, chitosan polyammonium salt, and carboxymethyl chitosan quaternary ammonium salt. The flocculant selected in this step has active hydroxyl and amino groups, has strong heavy metal adsorption and chelation effects, can make the chromium hydroxide precipitate have higher purity, and the flocculant can also dissolve in a slightly acidic environment, is harmless to the environment, and does not require secondary separation; the addition amount of the flocculant is 1 - 5 wt% of the mass of filtrate D.

[0024] The beneficial effects of the present invention are:

[0025] The present invention uses chromium-containing electroplating sludge, calcium carbonate, and quartz to prepare grossular ceramic green pigment by a solid-phase method, specifically conducts high-value application on chromium-containing sludge, effectively recovers other metals at the same time, and maximally realizes the full-component application of the sludge. The prepared pigment has good acid and alkali resistance, better environmental compatibility, and good overall performance.

[0026] The advantages of the present invention:

[0027] 1. The process of the present invention is simple, easy to operate. The prepared pigment has good color rendering performance, good acid and alkali resistance, and good economic benefits.

[0028] 2. The present invention selects common materials, has low cost, specifically realizes the resource utilization of chromium-containing sludge in the field of ceramic pigments, turns waste into treasure, and the waste liquid can be directly discharged, is harmless to the environment, and has good environmental benefits.

[0029] 3. Other heavy metals in the electroplating sludge have also been effectively recovered, which will neither cause heavy metal migration and endanger the environment nor generate certain economic benefits. Description of the Drawings

[0030] Figure 1 It is a process flow chart for preparing the ceramic colorant;

[0031] Figure 2 It is the XRD spectrum of the colorant sample in Example 1 before and after acid leaching and alkali leaching;

[0032] Figure 3 It is the XRD spectrum of the colorant samples prepared in Examples 1, 3, 5, 8, and 10;

[0033] Figure 4 It is the physical appearance diagram of the colorant powder in Example 1. Detailed Embodiments

[0034] The present invention will be further described below in conjunction with specific examples, but it is not limited to the content in the specification. Unless otherwise specified, "parts" mentioned in the examples are all parts by weight.

[0035] Figure 1 It is a schematic diagram of the method for recycling chromium-containing electroplating sludge resources of the present invention.

[0036] Ceramic colorants are an important part of the ceramic products field and also an important part of ceramic products or porcelain glazes and blanks. Chromium-based colorants are widely used, mainly including chromium oxide green colorants, chromium manganese green colorants, chromium aluminum red colorants, etc. Chromium-containing electroplating sludge contains a large amount of chromium. If calcium silicate substances are added, calcium chromium garnet green colorants with more stable color development can be prepared, and at the same time, they have good acid and alkali resistance.

[0037] The following specifically describes the preparation method and characteristics of the ceramic green colorant designed and implemented according to the present invention.

[0038] The chromium-based electroplating sludge used in the embodiments of the present invention comes from a certain electroplating factory in Jiangsu. After X-ray fluorescence spectrometry analysis (instrument model: XRF-1800), its main chemical components and contents are shown in Table 1:

[0039] Table 1 Composition of Chromium-Containing Electroplating Sludge

[0040] Main chemical components <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[Cr2O3]]> CaO CuO Content / wt% 0.23 0.53 5.39 83.01 1.30 1.09

[0041] Example 1

[0042] (1) Grind the electroplating sludge, dry it in a vacuum drying oven at 90 °C for 6 h, then pass it through a 100-mesh sieve, bag it for standby; weigh the dried electroplating sludge, calcium carbonate, silicon dioxide, and borax according to the ratio of 16:65:15:4, mix them thoroughly, place the mixture in a porcelain ark and put it in the center of the muffle furnace hearth, heat it to 1000 °C at a heating rate of 8 °C / min, and keep it warm for 60 min; turn off the power, take it out after cooling to room temperature with the furnace, and obtain solid powder 1;

[0043] (2) Acid-wash the powder 1 obtained in step (1) at room temperature, filter to obtain filtrate A and residue A, wash the residue A three times with deionized water until neutral, combine the washing liquid and filtrate A into filtrate B, and dry the washed residue A in a drying oven at 90 °C for 12 h to obtain grossularite ceramic green pigment; the acid solution is a mixture of hydrochloric acid, acetic acid, and water, the concentrations of hydrochloric acid and acetic acid are 20 g / L and 40 g / L respectively, and the volume ratio of the acid solution to the mass of powder 1 is 5 mL:1 g;

[0044] (3) Add 0.1 part of 100-mesh iron powder to the filtrate B obtained in step (2) in 5 portions, stir at room temperature for 20 min each time after adding, the stirring speed is 150 rpm, filter after full reaction to obtain copper powder and filtrate C;

[0045] (4) Add 35% hydrogen peroxide to the filtrate C obtained in step (3) in 3 portions, manually stir for 1 min each time after adding, stop adding hydrogen peroxide when no more bubbles are generated, slowly adjust the pH of the system to 4.5 with 10% ammonia water until no more red precipitate is formed; filter after the reaction is completed to obtain Fe(OH)3 and filtrate;

[0046] (5) Add 0.05 part of sodium metabisulfite to the filtrate D obtained in step (4) in 3 portions, stop adding sodium metabisulfite when no more green precipitate is generated, at the same time adjust the pH of the system to 8.5 with 10% ammonia water, add 2 wt% of chitosan based on the mass of filtrate D, stir at room temperature, filter to obtain Cr(OH)3 and waste liquid; dry the filter residue Cr(OH)3 and return it to the electroplating sludge in step (1) for reuse, and treat the remaining liquid as harmless liquid.

[0047] Example 2

[0048] The rest is the same as in Example 1, the difference is that in step (1), it is mixed evenly according to the ratio of 20 parts of electroplating sludge, 61 parts of calcium carbonate, 15 parts of silicon dioxide, and 4 parts of borax.

[0049] Example 3

[0050] The rest is the same as in Example 1, the difference is that in step (1), it is mixed evenly according to the ratio of 25 parts of electroplating sludge, 56 parts of calcium carbonate, 15 parts of silicon dioxide, and 4 parts of borax.

[0051] Example 4

[0052] The rest is the same as in Example 1, except that in step (1), 30 parts of electroplating sludge, 51 parts of calcium carbonate, 15 parts of silicon dioxide, and 4 parts of borax are mixed evenly.

[0053] Example 5

[0054] The rest is the same as in Example 1, except that in step (1), 30 parts of electroplating sludge, 56 parts of calcium carbonate, 10 parts of silicon dioxide, and 4 parts of borax are mixed evenly.

[0055] Example 6

[0056] The rest is the same as in Example 1, except that in step (1), the calcination temperature is adjusted to 900 °C.

[0057] Example 7

[0058] The rest is the same as in Example 1, except that in step (1), the calcination temperature is adjusted to 1100 °C.

[0059] Example 8

[0060] The rest is the same as in Example 1, except that in step (1), the calcination temperature is adjusted to 1200 °C.

[0061] Example 9

[0062] The rest is the same as in Example 8, except that in step (1), the borax is replaced with a compound mineralizer of borax and sodium fluorosilicate with equal mass and a mass ratio of 1:1.

[0063] Example 10

[0064] The rest is the same as in Example 8, except that in step (1), the borax is replaced with a compound mineralizer of borax and sodium fluorosilicate with equal mass and a mass ratio of 3:1.

[0065] Example 11

[0066] The rest is the same as in Example 8, except that in step (1), the borax is replaced with a compound mineralizer of borax and calcium fluoride with equal mass and a mass ratio of 1:1.

[0067] Example 12

[0068] The rest is the same as in Example 8, except that in step (1), the borax is replaced with a compound mineralizer of borax and sodium fluoride with equal mass and a mass ratio of 1:1.

[0069] Effect Example

[0070] 1. Acid / alkali resistance: The colorant samples prepared in the above-mentioned examples were respectively subjected to chromaticity testing and acid and alkali resistance testing. That is, they were respectively immersed in a 2 wt% hydrochloric acid solution and a 2 wt% sodium hydroxide solution, with a solid-liquid ratio of 1:40. After shaking vigorously for 5 min, they were filtered, washed until neutral, dried, and the chromaticity values before and after immersion were tested. The △E was calculated according to the formula △E = (△L* 2 +△a* 2 +△b* 2 ) 1 / 2 , where L*, a*, and b* are the indexes for evaluating the chromaticity value of the colorant, representing the lightness value, red-green value, and yellow-blue value respectively. △E is the index for the color difference between two colorants. The smaller △E is, the less obvious the color difference between the two colorants is, that is, the better the acid resistance and alkali resistance are. The results are shown in Table 2 below.

[0071] 2. Metal recovery rate: The main metal elements in filtrate A and the discharged sewage were quantitatively analyzed by inductively coupled plasma atomic emission spectrometry. The test instrument was the Optima5300D inductively coupled plasma atomic emission spectrometer of PerkinElmer Company, and the recovery rates η of copper, iron, and chromium were calculated according to the following formula Cu , η Fe , η Cr , %:

[0072]

[0073]

[0074]

[0075] In the formula, - the concentration of zinc ions in the discharged sewage, - the concentration of zinc ions in filtrate B, - the concentration of iron ions in the discharged sewage, - the concentration of zinc ions in filtrate B, - the concentration of chromium ions in the discharged sewage, - the concentration of chromium ions in filtrate B, g / L; V2 - the volume of the discharged sewage, V1 - the volume of filtrate B, L; The calculation results are shown in Table 2. The recovery rate of chromium ions is significantly higher than that of iron and zinc ions. This may be because the chromium content in the leachate in this example is higher. In actual production, appropriate hydrothermal reaction may result in better recovery effect.

[0076] Table 2

[0077] Item L* a* b* <![CDATA[Acid leaching △E1]]> <![CDATA[Alkaline leaching △E2]]> <![CDATA[η Cu％ > <![CDATA[η Fe％ > <![CDATA[η Cr％ > Example 1 44.35 -5.25 5.88 0.46 0.38 66.55 56.42 93.49 Example 2 43.34 -5.15 6.14 0.41 0.34 65.30 58.76 93.28 Example 3 41.69 -5.45 6.39 0.38 0.30 66.18 59.21 92.37 Example 4 48.69 -5.24 6.56 0.44 0.41 64.58 59.47 91.53 Example 5 47.26 -5.22 6.98 0.49 0.32 64.12 59.35 90.56 Example 6 46.56 -4.24 5.78 0.78 0.38 68.91 55.56 90.56 Example 7 45.45 -5.96 6.99 0.31 0.37 55.23 58.24 91.52 Example 8 49.56 -6.28 7.21 0.51 0.44 69.65 57.96 89.61 Example 9 48.55 -7.72 5.64 0.17 0.21 66.21 59.68 92.46 Example 10 48.66 -7.68 5.84 0.20 0.25 66.54 59.68 92.31 Example 11 48.25 -6.98 7.26 0.34 0.28 66.57 59.42 92.26 Example 12 49.22 -7.26 7.25 0.27 0.48 66.24 59.84 92.41

[0078] Figure 2It is the XRD patterns of the pigment sample before and after acid leaching and alkali leaching in Example 3. It can be found that its XRD pattern basically remains unchanged after acid leaching / alkali leaching, indicating that the uvarovite ceramic green pigment prepared by the method of the present invention is chemically stable and resistant to acids and alkalis.

[0079] Figure 3 They are the XRD patterns of the pigment samples of Examples 1, 3, 5, 8, and 10. It can be found that their main components all contain Ca3Cr2(SiO4)3, and there is also a small amount of unreacted SiO2. When a compound mineralizer is used, CaCrO4 is significantly reduced.

[0080] Figure 4 It is the uvarovite ceramic green pigment (Ca3Cr2(SiO4)3) prepared in Example 3.

[0081] In the above examples, the external sewage was detected, and it was found that the heavy metal leaching results met the national comprehensive sewage discharge standard (GB / T 8978-1996). Therefore, it will not have an adverse impact on the environment. The leaching results are shown in Table 3 (taking Example 1 as an example):

[0082] Table 3 Heavy metal leaching results

[0083] Concentration (mg / L) Total chromium <![CDATA[Cr 6+ > Cu Zn Pb Ni Sample 1.22 0.98 0.21 0.36 0.02 0.12 GB / T 8978-1996 1.5 0.5 0.5 2.0 1.0 1.0

[0084] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or changes made without departing from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for resource recovery of chromium-containing electroplating sludge, characterized in that, The steps include: (1) ball-milling chromium-containing electroplating sludge, drying the ground powder, and sieving to obtain electroplating sludge powder; weighing the electroplating sludge powder, calcium carbonate, silicon dioxide, and a mineralizer according to a certain ratio, fully mixing, calcining, cooling to room temperature, and then taking out to obtain a solid powder 1; the mineralizer is borax, or a mixture of borax and sodium fluorosilicate, in which the borax accounts for 50-75wt%; the mineralizer accounts for 2-10wt% of the total mass of the mixture, and the total mass of the mixture is the total mass of the electroplating sludge, calcium carbonate, silicon dioxide, and the mineralizer; (2) washing the powder 1 obtained in step (1) with acid at room temperature, filtering to obtain a filtrate A and a filter residue A, washing the filter residue A three times with deionized water until it becomes neutral, combining the washing liquid and the filtrate A to obtain a filtrate B, and drying the washed filter residue A to obtain a calcium chrome garnet ceramic green material; (3) Add iron powder to the filtrate B obtained in step (2), stir at room temperature, and filter after sufficient reaction to obtain copper powder and filtrate C; (4) Add hydrogen peroxide to the filtrate C obtained in step (3), and adjust the pH of the system to 4-5 until no red precipitate is generated. Filter to obtain Fe(OH)3 and filtrate D; (5) Sodium metabisulfite is added to the filtrate D obtained in step (4), and the pH value of the system is adjusted to 8-9. A flocculant is added, and the mixture is stirred at room temperature until no green precipitate is generated. The mixture is filtered to obtain Cr(OH)3 and waste liquid. The filter residue Cr(OH)3 is dried and returned to the electroplating sludge of step (1) for reuse. The remaining liquid is treated as a harmless liquid.

2. The resource recovery method according to claim 1, characterized in that, In step (1), the Cr content in the chromium-containing electroplating sludge is 35-60wt%.

3. The resource recovery method according to claim 1, characterized in that, In step (1), the calcium carbonate is replaced by or mixed with eggshell, shell, oyster shell biomass calcium source, and its amount is calculated as CaCO3; the mass ratio of the electroplating sludge, calcium carbonate, and silicon dioxide is 16-30: 51-65: 15-20.

4. The resource recovery method according to claim 1, characterized in that, In step (1), the mineralizer accounts for 4-6wt% of the total mass of the mixture.

5. The resource recovery method according to claim 1, characterized in that, In step (1), the sieving is through a 60-200 mesh sieve; the calcination temperature is 850-1200°C, the heating rate is 5-10°C / min, and the holding time is 30-180 min.

6. The resource recovery method according to claim 1, characterized in that, In step (2), the acid solution is a mixture of low-concentration hydrochloric acid, acetic acid and water, the concentrations of hydrochloric acid and acetic acid are 20-40 g / L and 30-50 g / L respectively, and the volume ratio of the acid solution to the mass ratio of the powder 1 is 3-5 mL: 1 g.

7. The resource recovery method according to claim 1, characterized in that, In step (3), the iron powder has a particle size of 100-200 meshes, and the iron powder is added in 3-8 batches. After each addition, stirring is performed for 15-40 min at a stirring speed of 150-300 rpm. When the iron powder in the monitoring system is no longer dissolved, the addition of iron powder is stopped.

8. The resource recovery method according to claim 1, characterized in that, In step (4), the concentration of hydrogen peroxide is 30-40%, and it is added in 3-5 batches. Stirring is performed for 1-2 minutes after each addition. When no bubbles are generated, the addition of hydrogen peroxide is stopped. The alkaline solution for adjusting the pH of the system is ammonia water with a concentration of 10-20wt%.

9. The resource recovery method according to claim 1, characterized in that, In step (5), the sodium metabisulfite is added in 3 - 5 batches, and the addition of sodium metabisulfite is stopped when no more green precipitate is produced; the alkaline solution for adjusting the pH of the system is ammonia water with a concentration of 10 - 20 wt%; the flocculant is selected from one or a combination of two or more of chitosan, hydroxymethyl chitosan, chitosan polyammonium salt, and carboxymethyl chitosan quaternary ammonium salt; the addition amount of the flocculant is 1 - 5 wt% of the mass of filtrate D.

10. The resource recovery method according to claim 9, characterized in that, The sodium metabisulfite and ammonia water are added simultaneously, and stirred for 1 - 2 min after each addition.

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