阅读说明：本技术 电镀污泥回收铬、铜、镍和钴的工艺 (Process for recovering chromium, copper, nickel and cobalt from electroplating sludge ) 是由 徐友良 周保学 李金花 于 2021-10-08 设计创作，主要内容包括：一种电镀污泥回收铬、铜、镍和钴的工艺,通过将含有铬、铁、铜、镍和钴的电镀污泥溶于强酸溶液并过滤后得到含有铬、铁、铜、镍、钴离子的滤液,经稀释后采用分阶段梯度浓度缓慢加入碱溶液反应,滤液pH由2.0调至4.0形成氢氧化铬沉淀和含有铁、铜、镍、钴离子的滤液,通过向滤液中缓慢加入碱溶液至pH达到4.50并通入空气形成含铁沉淀以及含有铜、镍、钴离子的滤液；通过向滤液中分阶段梯度浓度缓慢加入NaHCO-(3)溶液反应,pH由4.5调至5.5形成碳酸铜沉淀以及含有镍、钴离子和少量铜的滤液；再依次通过离子萃取和油相经反萃,分别得到含铜溶液、含镍溶液和含钴溶液。本发明具有回收率高、工艺简单、节能环保等特点。(A process for recovering chromium, copper, nickel and cobalt from electroplating sludge comprises the steps of dissolving electroplating sludge containing chromium, iron, copper, nickel and cobalt in a strong acid solution, filtering to obtain a filtrate containing chromium, iron, copper, nickel and cobalt ions, diluting, slowly adding an alkali solution in a stepwise gradient concentration manner for reaction, adjusting the pH of the filtrate from 2.0 to 4.0 to form chromium hydroxide precipitate and a filtrate containing iron, copper, nickel and cobalt ions, slowly adding an alkali solution into the filtrate until the pH reaches 4.50, and introducing air to form iron-containing precipitate and a filtrate containing copper, nickel and cobalt ions; NaHCO was slowly added to the filtrate by stepwise gradient concentration 3 The solution reacts, the pH is adjusted from 4.5 to 5.5 to form copper carbonate precipitate and the precipitate contains nickel and cobalt ions and a small amount of copperThe filtrate of (1); and then the copper-containing solution, the nickel-containing solution and the cobalt-containing solution are respectively obtained by ion extraction and oil phase back extraction in turn. The method has the characteristics of high recovery rate, simple process, energy conservation, environmental protection and the like.)

1. A process for recovering chromium, copper, nickel and cobalt from electroplating sludge, characterized in that the electroplating sludge containing chromium, iron, copper, nickel and cobalt is dissolved in a strong acid solution and filteredThen obtaining filtrate containing chromium, iron, copper, nickel and cobalt ions, diluting, slowly adding alkali solution in a staged gradient concentration manner for reaction, adjusting the pH of the filtrate from 2.0 to 4.0 to form chromium hydroxide precipitate and filtrate containing iron, copper, nickel and cobalt ions, slowly adding alkali solution into the filtrate until the pH reaches 4.50, and introducing air to form iron-containing precipitate and filtrate containing copper, nickel and cobalt ions; NaHCO was slowly added to the filtrate by stepwise gradient concentration₃The solution reacts, the pH is adjusted from 4.5 to 5.5 to form copper carbonate precipitate and filtrate containing nickel and cobalt ions and a small amount of copper; and then the copper-containing solution, the nickel-containing solution and the cobalt-containing solution are respectively obtained by ion extraction and oil phase back extraction in turn.

2. The process for recovering chromium, copper, nickel and cobalt from electroplating sludge as claimed in claim 1, wherein said step-wise gradient concentration slow addition of alkaline solution is: 3-5 stages are divided, the time for adding NaOH in each stage is controlled to be 2-4 hours, and the concentration C of NaOH added in the first stage₁The concentration gradient of the subsequent stages is controlled under the condition that the concentration is 0.4 to C_i/C_i-1Less than or equal to 0.8, wherein i represents the number of stages, the increment of pH control of the solution in each stage is delta pH which is approximately equal to 2/n, and n is the total stage times; stirring and filtering after the addition of NaOH is finished.

3. The process of claim 1, wherein said staged gradient of NaHCO is added slowly₃The solution is as follows: dividing into 3-5 stages, each stage of NaHCO₃The adding time is 2-4 hours, and NaHCO is added in the first stage₃Concentration C₁Is NaHCO with content of 5%₃The control condition of the concentration gradient of the solution and the subsequent stages is that C is more than or equal to 0.4_i/C_i-1Less than or equal to 0.8, wherein i represents the number of stages, the increment of pH control of the solution in each stage is delta pH which is approximately equal to 1/n, and n is the total stage times; addition of NaHCO₃After the reaction is finished, stirring and filtering.

4. The process for recovering chromium, copper, nickel and cobalt from electroplating sludge according to any one of claims 1 to 3, which is characterized by comprising the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: diluting the filtrate A obtained in the step 1) to Cr content³⁺The amount of the solution is 1-3%, the NaOH solution is slowly and uniformly added, the pH of the solution is finally adjusted to 4.0 from 2.0, chromium ions and NaOH react to form chromium hydroxide precipitate, and the adding process of the NaOH solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaOH is slowly added in each stage for 2-4 hours; the number of the stages of adding the NaOH solution is 3-5, and the concentration C of the NaOH added in the first stage is₁The concentration gradient of the subsequent stages is controlled under the condition that the concentration is 0.4 to C_i/C_i-1I is less than or equal to 0.8, i represents a certain stage, and the increment of pH control of the solution in each stage is that delta pH is approximately equal to 2/n; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide with uniformly dispersed particles, good crystallinity and low impurity content;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃The reaction forms a copper carbonate precipitate, in which NaHCO₃The adding process of the solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaHCO in each stage₃The slow addition time is 2-4 hours, and NaHCO₃The number of stages of solution addition may be 3-5, the NaHCO added in the first stage₃Concentration C₁Is NaHCO with content of 5%₃The control condition of the concentration gradient of the solution and the subsequent stages is that C is more than or equal to 0.4_i/C_i-1Less than or equal to 0.8 at each stageThe increment of the solution pH control is delta pH which is approximately equal to 1/n; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter pressing the precipitate to obtain a copper carbonate precipitate with uniformly dispersed particles, good crystallinity and low impurity content; the total copper recovered by the process is about 95%;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate E obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution of a compound for preparing copper and a salt thereof; the water phase is nickel-containing and cobalt-containing ion solution F;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions F obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution of a compound for preparing nickel and salts thereof; the water phase is cobalt ion-containing solution G;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the water phase from the water-phase cobalt ion-containing solution G obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain a cobalt-containing solution of the compound for preparing cobalt and the salt thereof.

Technical Field

The invention relates to a technology in the field of heavy metal recovery, in particular to a process for recovering chromium, copper, nickel and cobalt from electroplating sludge.

Background

The existing resource utilization method of electroplating heavy metal sludge mainly comprises an acid leaching method, an ammonia leaching method, a biological leaching method, a roasting leaching method, a smelting method and the like; for example, in the prior art, the electroplating sludge is roasted by medium and low temperature alkali, chromium in the electroplating sludge is converted into Cr (VI), and chromate is recovered, however, the recovery rate of the technology is low, the converted Cr (VI) acid salt is toxic and harmful, Cr (VI) can further enter the sludge after reaction to form a new pollution source, and the technology is not beneficial to further recovering other metals in the electroplating sludge, such as copper, nickel, cobalt and the like. On the other hand, the electroplating sludge has complex sources, different heavy metal contents and existing forms, but most of the prior art focuses on the recovery of one or a few heavy metal ions, and lacks a comprehensive, systematic and efficient resource utilization separation process, so that new pollution or waste is generated in the recovery process, and the problems of few heavy metal types, low recovery rate, high impurity content, low purity, heavy secondary pollution, high cost, complex operation, unstable operation and the like are caused.

Disclosure of Invention

The invention provides a process for recovering chromium, copper, nickel and cobalt from electroplating sludge, which aims at solving the problems of few heavy metal types, low recovery rate, high impurity content, low purity, heavy secondary pollution, high cost, complex operation, unstable operation and the like in the existing electroplating sludge recovery technology, and has the characteristics of high recovery rate, simple process, energy conservation, environmental protection and the like.

The invention is realized by the following technical scheme:

the invention relates to a process for recovering chromium, copper, nickel and cobalt from electroplating sludge, which is obtained by dissolving electroplating sludge containing chromium, iron, copper, nickel and cobalt in strong acid solution and filteringDiluting the filtrate containing chromium, iron, copper, nickel and cobalt ions, slowly adding an alkali solution in a stepwise gradient concentration manner for reaction, adjusting the pH of the filtrate from 2.0 to 4.0 to form chromium hydroxide precipitate and the filtrate containing iron, copper, nickel and cobalt ions, slowly adding the alkali solution into the filtrate until the pH reaches 4.50, and introducing air to form iron-containing precipitate and the filtrate containing copper, nickel and cobalt ions; NaHCO was slowly added to the filtrate by stepwise gradient concentration₃The solution reacts, the pH is adjusted from 4.5 to 5.5 to form copper carbonate precipitate and filtrate containing nickel and cobalt ions and a small amount of copper; and then the copper-containing solution, the nickel-containing solution and the cobalt-containing solution are respectively obtained by ion extraction and oil phase back extraction in turn.

The slow addition of the alkali solution in a staged gradient concentration refers to that: 3-5 stages are divided, the time for adding NaOH in each stage is controlled to be 2-4 hours, and the concentration C of NaOH added in the first stage₁The concentration gradient of the subsequent stages is controlled under the condition that the concentration is 0.4 to C_i/C_i-1Less than or equal to 0.8, wherein i represents the number of stages, the increment of pH control of the solution in each stage is delta pH which is approximately equal to 2/n, and n is the total stage times; stirring and filtering after the addition of NaOH is finished.

Said staged gradient concentration slowly adding NaHCO₃The solution is as follows: dividing into 3-5 stages, each stage of NaHCO₃The adding time is 2-4 hours, and NaHCO is added in the first stage₃Concentration C₁Is NaHCO with content of 5%₃The control condition of the concentration gradient of the solution and the subsequent stages is that C is more than or equal to 0.4_i/C_i-1Less than or equal to 0.8, wherein i represents the number of stages, the increment of pH control of the solution in each stage is delta pH which is approximately equal to 1/n, and n is the total stage times; addition of NaHCO₃After the reaction is finished, stirring and filtering.

The method specifically comprises the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: diluting the filtrate A obtained in the step 1) to Cr content³⁺1-3% of the total amount of the components are slowly and uniformly addedAdding NaOH solution, adjusting the pH of the solution from 2.0 to 4.0 at last, and reacting chromium ions with NaOH to form chromium hydroxide precipitate, wherein the adding process of the NaOH solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaOH is slowly added in each stage for 2-4 hours; the number of the stages of adding the NaOH solution is 3-5, and the concentration C of the NaOH added in the first stage is₁The concentration gradient of the subsequent stages is controlled under the condition that the concentration is 0.4 to C_i/C_i-1Less than or equal to 0.8(i represents a certain stage), and the increment of pH control of the solution in each stage is that delta pH is approximately equal to 2/n; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide with uniformly dispersed particles, good crystallinity and low impurity content;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃The reaction forms a copper carbonate precipitate, in which NaHCO₃The adding process of the solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaHCO in each stage₃The slow addition time is 2-4 hours, and NaHCO₃The number of stages of solution addition may be 3-5, the NaHCO added in the first stage₃Concentration C₁Is NaHCO with content of 5%₃The control condition of the concentration gradient of the solution and the subsequent stages is that C is more than or equal to 0.4_i/C_i-1Less than or equal to 0.8(i represents a certain stage), and the increment of pH control of the solution in each stage is that delta pH is approximately equal to 1/n; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter pressing the precipitate to obtain a copper carbonate precipitate with uniformly dispersed particles, good crystallinity and low impurity content; the total copper recovered by the process is about 95%;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate E obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution of a compound for preparing copper and a salt thereof; the water phase is nickel-containing and cobalt-containing ion solution F;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions F obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution of a compound for preparing nickel and salts thereof; the water phase is cobalt ion-containing solution G;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the water phase from the water-phase cobalt ion-containing solution G obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain a cobalt-containing solution of the compound for preparing cobalt and the salt thereof.

Drawings

FIG. 1 is a schematic view of the preparation process of the present invention.

Detailed Description

Example 1

The embodiment specifically comprises the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: diluting the filtrate A obtained in the step 1) to Cr content³⁺The amount of the solution is 2 percent, the NaOH solution is slowly and uniformly added, the pH value of the solution is finally adjusted to 4.0 from 2.0, chromium ions and NaOH react to form chromium hydroxide precipitate, the adding process of the NaOH solution adopts staged gradient concentration addition, and the method specifically comprises the following steps: NaOH is slowly added in each stage for 3 hours; the number of stages of adding NaOH solution is n-4, and the concentration C of NaOH added in the first stage₁The pH value of the NaOH solution with the content of 5 percent is adjusted to 2.5; the control conditions of the concentration gradient in each subsequent stage are the second stage C₂NaOH content of 3.5%, pH adjusted to 3.0, third stage C₃pH 3.5 with 2% NaOH, fourth stage C₄NaOH with the content of 1 percent, and the pH value is adjusted to 4.0; stirring and filtering after the NaOH is added, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain uniformly dispersed particlesChromium hydroxide which is uniform, has good crystallinity and low impurity content and is easy to dissolve in weak acid;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃Reacting to form copper carbonate precipitate; NaHCO 2₃The solution is added by adopting a step-by-step gradient concentration, and each step of NaHCO is adopted₃Slowly adding for 3 hours; NaHCO 2₃The solution is added in four stages, NaHCO added in the first stage₃Concentration of 5%, pH was adjusted from 4.50 to 4.75, and NaHCO was added in the second stage₃Concentration of 3%, pH adjusted from 4.75 to 5.00, NaHCO added in the third stage₃Concentration of 2%, pH adjusted from 5.00 to 5.25, NaHCO added in the fourth stage₃The concentration content is 1 percent, and the pH value is adjusted from 5.25 to 5.50; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter pressing the precipitate to obtain a copper carbonate precipitate with uniformly dispersed particles, good crystallinity and low impurity content; the total copper recovered by the process is about 95%;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate E obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution; the water phase is nickel-containing and cobalt-containing ion solution F;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions F obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution; the water phase is cobalt ion-containing solution G;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the water phase from the water-phase cobalt ion-containing solution G obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain a cobalt-containing solution.

The purity of the chromium hydroxide prepared by the embodiment is more than 99%, the chromium hydroxide can be dissolved in 6mol/L acetic acid, the purity of copper carbonate is more than 99%, and the recovery rate of chromium, copper, nickel and cobalt in electroplating sludge is 99%.

The effects of example 1 are described below in terms of 4 comparative examples.

Comparative example 1

The comparative example specifically included the following steps:

step 1) heavy metal leaching: dissolving electroplating sludge in a strong acid solution, and stirring for reaction, wherein the dissolved pH value is 2; filtering to obtain filtrate containing chromium, iron, copper, nickel and cobalt ions, and separating solid from liquid;

step 2) precipitation separation of chromium: diluting the filtrate obtained in the step 1) to Cr content³⁺Adding 20% NaOH solution into the filtrate until the pH value is 4, and stirring to react for 0.5h to obtain chromium hydroxide precipitate; washing and filter pressing to obtain filtrate containing iron, copper, nickel and cobalt ions, and separating solid from liquid;

step 3) removing iron impurities: adding a 20% NaOH solution into the filtrate obtained in the step 2) until the pH value is 4.5, introducing air, stirring for 0.5h, precipitating iron ions, and filtering to obtain a filtrate containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: adding 20% NaHCO into the filtrate obtained in step 3)₃The solution is adjusted to pH5.5, the reaction time is 0.5h, copper carbonate precipitation is obtained, and the filtration is carried out, thus obtaining the filtrate containing a small amount of copper, nickel and cobalt ions;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution; the water phase is nickel-containing and cobalt-containing ion solution;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions from the aqueous phase obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution; the water phase is a cobalt ion-containing solution;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the aqueous phase from the aqueous phase cobalt ion-containing solution obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain the cobalt ion-containing solution.

The purity of the chromium hydroxide precipitate prepared in the comparative example is 93%, the chromium hydroxide can hardly be dissolved in 6mol/L acetic acid (< 5%), the purity of the copper carbonate precipitate is 92%, and the recovery rates of chromium, copper, nickel and cobalt in the electroplating sludge are 85%, 86%, 80% and 79%, respectively.

Comparative example 2

The comparative example specifically included the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: filtrate A and filtrate Cr obtained in step 1)³⁺The amount of 6 percent, slowly and uniformly adding NaOH solution, adjusting the pH of the solution from 2.0 to 4.0, reacting chromium ions with NaOH to form chromium hydroxide precipitate, wherein the adding process of the NaOH solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaOH is slowly added in each stage for 3 hours; the number of stages of adding NaOH solution is n-4, and the concentration C of NaOH added in the first stage₁The pH value of the solution is adjusted to 2.5 by using NaOH solution with the content of 20 percent; the control conditions of the concentration gradient in each subsequent stage are the second stage C₂pH of 15% NaOH, 3.0, third stage C₃pH 3.5 with 7.5% NaOH, fourth stage C₄NaOH with the content of 3.5 percent, and the pH value is adjusted to 4.0; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃Reacting to form copper carbonate precipitate; NaHCO 2₃The solution is added by adopting a step-by-step gradient concentration, and each step of NaHCO is adopted₃Slowly adding for 3 hours; NaHCO 2₃The solution is added in four stages, NaHCO added in the first stage₃Concentration of 20%, pH was adjusted from 4.50 to 4.75, and NaHCO was added in the second stage₃Concentration of 12%, pH adjusted from 4.75 to 5.00, NaHCO added in the third stage₃The concentration is 8%, the pH is adjusted from 5.00 to 5.25, NaHCO is added in the fourth stage₃The concentration content is 4 percent, and the pH value is adjusted from 5.25 to 5.50; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter-pressing the precipitate to obtain a copper carbonate precipitate;

the purity of the chromium hydroxide precipitate prepared in the comparative example is 97%, the solubility of chromium hydroxide in 6mol/L acetic acid is low (< 20%), and the purity of the copper carbonate precipitate is 97%.

Comparative example 3

The comparative example specifically included the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: filtrate A and filtrate Cr obtained in step 1)³⁺The amount of 6 percent, slowly and uniformly adding NaOH solution, adjusting the pH of the solution from 2.0 to 4.0, reacting chromium ions with NaOH to form chromium hydroxide precipitate, wherein the adding process of the NaOH solution adopts staged gradient concentration addition, and specifically comprises the following steps: NaOH is slowly added in each stage for 3 hours; the number of stages of adding NaOH solution is n-4, and the concentration C of NaOH added in the first stage₁The pH value of the solution is adjusted to 2.5 by using NaOH solution with the content of 20 percent; the control conditions of the concentration gradient in each subsequent stage are the second stage C₂pH of 15% NaOH, 3.0, third stage C₃pH 3.5 with 7.5% NaOH, fourth stage C₄NaOH with the content of 3.5 percent, and the pH value is adjusted to 4.0; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: adding 10% NaOH solution into the filtrate D obtained in the step 3), finally adjusting the pH of the solution from 4.5 to 7, stirring at the speed of 10 r/min for 0.5h, and reacting copper ions with NaOH to form copper hydroxide precipitate.

The purity of the copper hydroxide precipitate prepared in this comparative example was 85%.

Comparative example 4

The comparative example specifically included the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: slowly and uniformly adding 30% H into the filtrate A obtained in the step 1)₂O₂And 6mol/LNaOH solution, stirring, adjusting the pH value of the solution to 11, Cr³⁺Oxidation of ions to Cr⁶⁺Is converted into Na₂CrO₄The solution is obtained by converting iron, copper, nickel and cobalt ions into hydroxide precipitate and filtering part of chromate precipitate, and the filtrate is Na₂CrO₄And (3) solution.

The recovery rate of chromium in the electroplating sludge of the comparative example is 83 percent.

Example 2

The embodiment specifically comprises the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain a filter A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: diluting the filtrate A obtained in the step 1) to Cr content³⁺Adding NaOH solution slowly and uniformly, adjusting the pH of the solution from 2.0 to 4.0 finally, and reacting chromium ions with NaOH to form chromium hydroxide precipitate; the addition process of NaOH solution adopts staged gradient concentration addition, each timeNaOH is slowly added in the stage for 4 hours; the stage of adding NaOH solution is divided into n-3, and the concentration C of NaOH added in the first stage₁The pH was adjusted to 2.6 for a 5% NaOH solution, and the conditions for controlling the concentration gradient in each stage were the second stage C₂NaOH with a content of 2.5%, pH adjusted to 3.3, third stage C₃NaOH with the content of 1 percent, and the pH value is adjusted to 4.0; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide with uniformly dispersed particles, good crystallinity and low impurity content;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃Reacting to form copper carbonate precipitate; NaHCO 2₃The solution is added by adopting a step-by-step gradient concentration, and each step of NaHCO is adopted₃Slowly adding for 4 hours; NaHCO 2₃The solution is added in 3 stages, NaHCO added in the first stage₃Concentration of 5%, pH was adjusted from 4.50 to 4.83, and NaHCO was added in the second stage₃Concentration of 2.5%, pH adjusted from 4.83 to 5.16, NaHCO added in the third stage₃The concentration content is 1 percent, and the pH value is adjusted from 5.16 to 5.50; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter pressing the precipitate to obtain a copper carbonate precipitate with uniformly dispersed particles, good crystallinity and low impurity content; the total copper recovered by the process is about 95%;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate E obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution; the water phase is nickel-containing and cobalt-containing ion solution F;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions F obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution; the water phase is cobalt ion-containing solution G;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the water phase from the water-phase cobalt ion-containing solution G obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain a cobalt-containing solution.

The purity of the chromium hydroxide prepared by the embodiment is 99%, the chromium hydroxide can be dissolved in 6mol/L acetic acid, the purity of copper carbonate is 99%, and the recovery rate of chromium, copper, nickel and cobalt in electroplating sludge is 98%.

Example 3

The embodiment specifically comprises the following steps:

step 1) heavy metal leaching: dissolving the electroplating sludge in a strong acid solution, stirring for reaction, wherein the dissolution pH value is 2.0; filtering to separate insoluble solid residue from the solution to obtain filtrate A containing chromium, iron, copper, nickel and cobalt ions;

step 2) precipitation separation of chromium: diluting the filtrate A obtained in the step 1) to Cr content³⁺The amount of the solution is 3 percent, the NaOH solution is slowly and uniformly added, the pH value of the solution is finally adjusted to 4.0 from 2.0, chromium ions and NaOH react to form chromium hydroxide precipitate, the adding process of the NaOH solution adopts staged gradient concentration addition, and the method specifically comprises the following steps: NaOH is slowly added in each stage for 2 hours; the stage of adding NaOH solution is divided into n-5, and the concentration C of NaOH added in the first stage₁The pH value of the solution is adjusted to 2.4 by 5 percent NaOH solution; the control conditions of the concentration gradient in each subsequent stage are the second stage C₂pH of 4% NaOH, adjusted to 2.8, third stage C₃pH 3.2 with 3% NaOH, fourth stage C₄A pH of 3.6 with 2% NaOH, a fifth stage C₅NaOH with the content of 1 percent, and the pH value is adjusted to 4.0; stirring and filtering after the addition of NaOH is finished, wherein the filtrate is a filtrate B containing iron, copper, nickel and cobalt ions, and washing and filter-pressing the precipitate to obtain chromium hydroxide with uniformly dispersed particles, good crystallinity and low impurity content;

step 3) removing iron impurities: slowly and uniformly adding a 3% NaOH solution into the filtrate B obtained in the step 2) until the pH value is 4.50, introducing air, slowly stirring for reacting for 5 hours, converting iron ions into precipitates, and filtering to obtain a filtrate D containing copper ions, nickel ions and cobalt ions;

step 4) copper precipitation separation: slowly and uniformly adding NaHCO into the filtrate D obtained in the step 3)₃The pH of the solution is finally adjusted to 5.5 from 4.5, and copper ions and NaHCO are added₃Reacting to form copper carbonate precipitate; NaHCO 2₃The solution is added by adopting a step-by-step gradient concentration, and each step of NaHCO is adopted₃Slowly adding for 2 hours; NaHCO 2₃The solution is added in 5 stages, NaHCO added in the first stage₃Concentration of 5%, pH was adjusted from 4.50 to 4.70, and NaHCO was added in the second stage₃Concentration of 4%, pH adjusted from 4.70 to 4.90, NaHCO added in the third stage₃Concentration of 3%, pH adjusted from 4.90 to 5.10, NaHCO added in the fourth stage₃The concentration content is 2 percent, and the pH value is adjusted from 5.10 to 5.30; NaHCO added in the fifth stage₃The concentration content is 1 percent, and the pH value is adjusted from 5.30 to 5.50; addition of NaHCO₃After the reaction is finished, stirring and filtering, wherein the filtrate is a filtrate E containing nickel and cobalt ions and a small amount of copper, and washing and filter pressing the precipitate to obtain a copper carbonate precipitate with uniformly dispersed particles, good crystallinity and low impurity content; the total copper recovered by the process is about 95%;

step 5) copper extraction separation: extracting the residual copper ions in the filtrate E obtained in the step 4) by using the existing copper ion extracting agent, and performing back extraction on the oil phase to obtain a copper-containing solution; the water phase is nickel-containing and cobalt-containing ion solution F;

step 6) extraction and separation of nickel: extracting nickel ions in the aqueous phase containing nickel and cobalt ions F obtained in the step 5) by using the conventional nickel ion extracting agent, and performing back extraction on the oil phase to obtain a nickel-containing solution; the water phase is cobalt ion-containing solution G;

step 7) extraction and separation of cobalt: extracting the cobalt ions in the water phase from the water-phase cobalt ion-containing solution G obtained in the step 6) by using the existing cobalt ion extracting agent, and performing back extraction on the oil phase to obtain a cobalt-containing solution.

The purity of the chromium hydroxide prepared by the embodiment is 99%, the chromium hydroxide can be dissolved in 6mol/L acetic acid, the purity of copper carbonate is 99%, and the recovery rate of chromium, copper, nickel and cobalt in electroplating sludge is 99%.

Compared with the prior art, the separation process sequence of the method avoids mutual interference among separated ions to the maximum extent. In the prior art, a process of sintering trivalent chromium at a medium-low temperature and alkalinity to generate hexavalent chromium or oxidizing the trivalent chromium into the hexavalent chromium by a strong hydrogen peroxide oxidizer in a water phase system is usually selected, and the soluble trivalent chromium is used for separating the trivalent chromium, but the hexavalent chromium generated by the processes has high toxicity, so that the subsequent separation process is polluted and sludge hazardous waste is generated. The method comprises the steps of firstly separating chromium ions from other metal ions in a chromium hydroxide precipitation form, then separating iron ions by air oxidation, then separating most of copper ions by copper carbonate precipitation, and finally separating the rest copper, nickel and cobalt ions by an extraction and back extraction process. In addition, in the separation process, ammonia (amine) precipitants are not adopted to generate hydroxide precipitates, and sulfide precipitates are not adopted to be sulfide processes, so that ammonia nitrogen sewage discharge and virulent hydrogen sulfide discharge are avoided; the oxygen is used as the oxidant to remove iron, so that the method is green and pollution-free.

In the process of the method, the separation efficiency of the trivalent chromium is high, the obtained chromium hydroxide precipitate has high purity and few coprecipitation impurity ions, is easy to dissolve in weak acid, and can be widely used for preparing trivalent chromium weak acid salt. Although the existing trivalent chromium hydroxide precipitation process also adopts an alkali precipitation process, the prior art adopts a method of directly adding alkali precipitation into a trivalent chromium salt solution to prepare chromium hydroxide, the alkali concentration is difficult to uniformly control in the reaction process, the pH change range is wide, and the partial pH even reaches>7, the mutual aggregation, cross-linking and aging among particles are caused to form large-particle chromium hydroxide precipitate which is difficult to dissolve in weak acid (such as acetic acid) and form Cr³⁺With Fe³⁺、Ni²⁺、Cu²⁺Coprecipitation of the hydroxide of (1); despite the use of low Cr concentration³⁺Reacting with low-concentration alkali solution or mixing alkali solution with Cr³⁺Simultaneously adding into water is beneficial to reducing the cross-linking and aggregation of chromium hydroxide precipitate, but the Cr with too low concentration³⁺The alkali liquor consumes a large amount of water, and the problem of uneven alkali distribution in the reaction process or the later stage of the reaction cannot be solvedCross-linking and aggregation problems; and the ammonia (amine) precipitator is adopted, so that the problem of ammonia nitrogen sewage discharge is caused. In the addition process of the sodium hydroxide precipitant, the invention adopts lower heavy metal ion concentration, controls the precipitation pH to be always within the range of 2-4, further controls the increase change of the pH according to the metal ion concentration and the reaction process of each stage, and effectively realizes the alkali concentration and Cr of each stage in the reverse process by the process of adding alkali concentration in stages, long time and gradient³⁺The concentration is effectively matched and controlled, so that the problem that local pH is changed violently possibly, particularly the alkalinity at the final stage of the reaction is relatively overhigh is solved, the overall pH fluctuation in the reaction process is small, the reaction is slow and mild, the crystallization time is long, and the obtained precipitate has the advantages of fine granularity, uniform dispersion, good and uniform crystallinity, high purity and easy dissolution in weak acid.

The copper carbonate precipitate obtained by the method has high purity and uniform and consistent precipitate. At present, the separation of copper ions mainly adopts a copper hydroxide precipitation process, but sodium hydroxide is strong alkali, so that Cu is easily caused²⁺、Ni²⁺To influence Cu (OH)₂Purity and crystalline morphology of; the method selects HCO with weak alkalinity₃ ^-Instead of OH^-The precipitating agent is a precipitator, the pH value of the precipitate is controlled to be in the range of 4.5-5.5 all the time, and the concentration fluctuation of the precipitating agent is small, the reaction is slow, the crystallization time is long, and Cu cannot be caused by long-time addition process of low heavy metal ion concentration, low alkali concentration and gradient concentration²⁺、Ni²⁺The coprecipitation and the precipitation are uniform and consistent.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.