Method for removing hexavalent chromium in laterite-nickel ore high-pressure acid leaching process

Abstract

The invention provides a method for removing hexavalent chromium in a laterite-nickel ore high-pressure acid leaching process. According to the method, after a CCD countercurrent washing step, CCD overflow liquid is obtained; whether hexavalent chromium ions exist or not is judged according to the b value of the LAB color mode of the CCD overflow liquid, and the concentration of the hexavalent chromium ions in the CCD overflow liquid is detected according to the potential value of the CCD overflow liquid; secondly, adding a reducing agent into the CCD overflow liquid, and enabling the CCD overflow liquid added with the reducing agent to enter a first-stage iron and aluminum removal step; optionally, after the first-stage iron and aluminum removal step, whether hexavalent chromium ions exist or not is judged according to the b value of the LAB color mode of the liquid obtained after first-stage iron and aluminum removal, if yes, the concentration of the hexavalent chromium ions in the liquid is detected according to the potential value of the liquid obtained after first-stage iron and aluminum removal, and a reducing agent continues to be added into the liquid obtained after first-stage iron and aluminum removal. The problems that in the laterite-nickel ore high-pressure acid leaching process, the chromium content is not detected in time, the using amount of a reducing agent for removing hexavalent chromium is large, and efficiency is low are solved.

Description

Technical Field

[0001] The invention relates to the technical field of laterite nickel ore, and in particular to a method for removing hexavalent chromium in a high-pressure acid leaching process of laterite nickel ore. Background Art

[0002] The high-pressure acid leaching process is usually used to prepare nickel-cobalt hydroxide from laterite nickel ore, which mainly consists of high-pressure acid leaching (usually 2-5MPa), cyclic leaching, pre-neutralization, CCD countercurrent washing, one-stage iron and aluminum removal, two-stage iron and aluminum removal, one-stage nickel-cobalt precipitation, and two-stage nickel-cobalt precipitation. Some laterite nickel ores will produce hexavalent chromium in the high-pressure acid leaching process, and finally produce nickel-cobalt hydroxide products containing hexavalent chromium, and the presence of hexavalent chromium will affect the product performance of nickel-cobalt hydroxide. Compared with qualified nickel-cobalt hydroxide products, nickel-cobalt hydroxide products containing hexavalent chromium have the following defects: low nickel, high manganese, high chromium, high water content, and increased transportation and handling costs; in the process of producing nickel-cobalt hydroxide products containing hexavalent chromium, the first stage of iron-aluminum slag will carry hexavalent chromium, which directly leads to excessive hexavalent chromium in the tailings slurry and cannot meet the emission standards.

[0003] At present, after the existing process produces hexavalent chromium during the high-pressure leaching reaction of laterite nickel ore and finally obtains unqualified nickel cobalt hydroxide products containing hexavalent chromium, the product is usually removed from hexavalent chromium by downstream enterprises or departments. At present, the method for treating nickel cobalt hydroxide containing hexavalent chromium in production is acid dissolution, adding reagents to convert hexavalent chromium into trivalent chromium, and then using liquid alkali to adjust the pH value of the slurry to precipitate and remove trivalent chromium. However, a certain amount of nickel precipitation will be lost while removing chromium, and the treatment of this part of hexavalent chromium will increase additional processes and costs. In addition, there is a process in which different types of reducing agents are added during high-pressure acid leaching, circulating leaching, pre-neutralization, CCD countercurrent washing, one-stage iron and aluminum removal, and two-stage iron and aluminum removal, but it can only explain the types of available reducing agents and the corresponding effects, which is somewhat disconnected from actual production. In actual production, it takes a certain amount of time to sample and test the hexavalent chromium content in the solution on site. If the best time is delayed, the quality of a batch of nickel cobalt hydroxide products (MHP products) will be affected and cannot be recovered. If it is unknown whether hexavalent chromium will be produced in the liquid after high-pressure leaching during production, it is impossible to predict the amount of reducing chromium removal agent that should be added first. If the amount of agent is too small, the hexavalent chromium cannot be completely removed; if the amount of agent is too large, the reduction will be excessive, and the trivalent iron in the system will be reduced to divalent iron. When removing iron and aluminum, divalent iron is more difficult to remove than trivalent iron, which will increase the pressure of subsequent iron and aluminum removal, and too high a divalent iron content will increase the corrosion of the equipment.

[0004] Based on the above reasons, a method is needed that does not affect the original process flow of the high-pressure acid leaching process of laterite nickel ore, can quickly detect and remove chromium, and has a relatively accurate amount of chromium removal. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for removing hexavalent chromium in a high-pressure acid leaching process of laterite nickel ore, so as to solve the problems in the prior art that the chromium content is not detected in time in the high-pressure acid leaching process of laterite nickel ore, and the amount of reducing agent used for removing hexavalent chromium is large and the efficiency is low.

[0006] In order to achieve the above-mentioned object, according to one aspect of the present invention, a method for removing hexavalent chromium in a high-pressure acid leaching process of laterite nickel ore is provided, wherein the high-pressure acid leaching process of laterite nickel ore comprises a high-pressure acid leaching step, a circulating leaching step, a neutralization step, a CCD countercurrent washing step, a first-stage iron and aluminum removal step, a second-stage iron and aluminum removal step, and a nickel and cobalt precipitation step, wherein after the CCD countercurrent washing step, a CCD overflow liquid is obtained; whether hexavalent chromium ions exist is determined according to the b value of the LAB color mode of the CCD overflow liquid, and the hexavalent chromium ion concentration in the CCD overflow liquid is detected according to the potential value of the CCD overflow liquid; secondly, a reducing agent is added to the CCD overflow liquid, and then the CCD overflow liquid to which the reducing agent is added is allowed to flow; The liquid enters a first iron and aluminum removal step; wherein, the amount of reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the CCD overflow liquid are reduced to trivalent chromium ions, and does not exceed 1.5 times the theoretical amount; optionally, after the first iron and aluminum removal step, a first iron and aluminum removal liquid is obtained, and whether hexavalent chromium ions exist is determined according to the b value of the LAB color mode of the first iron and aluminum removal liquid. If so, the hexavalent chromium ion concentration therein is detected according to the potential value of the first iron and aluminum removal liquid, and the reducing agent is continued to be added to the first iron and aluminum removal liquid; wherein, the amount of reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the first iron and aluminum removal liquid are reduced to trivalent chromium ions, and does not exceed 1.5 times the theoretical amount.

[0007] Further, the step of detecting the hexavalent chromium ion concentration in the CCD overflow liquid or the liquid after the iron and aluminum removal according to the potential value includes: preparing reference solutions with different hexavalent chromium concentrations, and other cations in the reference solution besides hexavalent chromium are Ni ions, Fe 3+ Ions and Al 3+ ions; the Ag / AgCl potential of each reference solution is tested, and a relationship curve between the hexavalent chromium concentration and the Ag / AgCl potential is obtained; the Ag / AgCl potential of the CCD overflow liquid or the liquid after a section of iron and aluminum removal is tested by a potentiometer, and the potential is brought into the relationship curve to obtain the hexavalent chromium ion concentration of the CCD overflow liquid or the liquid after a section of iron and aluminum removal.

[0008] Furthermore, the concentrations of other cations in the reference solution are: Ni ion 5g / L, Fe 2+ Ions 0.5~5g / L and Al 3+ Ions are 0.3-4 g / L, and its pH value is 4-5.

[0009] Furthermore, in the process of detecting the Ag / AgCl potential of the standard solution, the temperature of the standard solution is maintained to be the same as the temperature of the CCD countercurrent washing; preferably, the temperature of the standard solution is maintained at 70-80°C.

[0010] Furthermore, the step of judging whether hexavalent chromium ions exist according to the b value of the LAB color mode of the CCD overflow liquid or the liquid after a section of iron and aluminum removal includes: measuring the b value of the CCD overflow liquid or the liquid after a section of iron and aluminum removal in the LAB color mode by using a colorimeter, wherein when the b value is a positive number, it indicates the presence of hexavalent chromium ions, and the larger the b value, the higher the concentration of hexavalent chromium ions.

[0011] Furthermore, the amount of the reducing agent added is 1 to 1.3 times the theoretical amount for reducing hexavalent chromium ions in the CCD overflow liquid to trivalent chromium ions.

[0012] Further, the reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, sodium thiosulfate, sulfur, and sodium sulfide; preferably, the reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, and sodium thiosulfate.

[0013] Furthermore, the first iron and aluminum removal step includes: adjusting the pH value of the CCD overflow liquid to which the reducing agent is added to 2.0-5.0, introducing oxygen-containing gas, and then reacting at 55-90° C. for 10 min-20 h.

[0014] Furthermore, the second stage iron and aluminum removal step comprises: introducing oxygen-containing gas into the reaction solution obtained in the first stage iron and aluminum removal step, adjusting the pH value to 4.0-6.0, and then reacting at 45-80° C. for 10 min-20 h.

[0015] Furthermore, in the first stage iron and aluminum removal step and the second stage iron and aluminum removal step, each independently: one or more of calcium carbonate, sodium hydroxide, calcium hydroxide, and calcium oxide are used as pH regulators; preferably, the oxygen-containing gas is air or oxygen.

[0016] By applying the technical solution of the present invention, a method is provided which does not affect the high-pressure acid leaching process of laterite nickel ore, and can realize rapid detection, rapid reduction and removal of hexavalent chromium ions. It is known from the study of the high-pressure acid leaching process of laterite nickel ore in the prior art that if the neutralization step is carried out with residual ore, the residual ore itself will produce a part of divalent iron ions, and the divalent iron ions can reduce a part of the hexavalent chromium ions. Therefore, the present invention selects to qualitatively and quantitatively test the hexavalent chromium content according to the b value and potential value of the LAB color mode after the CCD countercurrent washing step, and then add a reducing agent to the obtained CCD overflow liquid, so that chromium can be removed using relatively less reducing agent. And after the CCD countercurrent washing, chromium can be further removed in a further iron and aluminum removal step.

[0017] The present invention can combine the potential value of the CCD overflow liquid and the optional liquid after the iron and aluminum removal with the b value of the LAB color mode to quickly and semi-quantitatively determine the concentration of hexavalent chromium and control the amount of the reducing agent. Only by adding a reducing agent that is no more than 1.5 times the theoretical amount, the purpose of removing hexavalent chromium ions can be well achieved. In the whole process, the range of the amount of the reducing agent can be predicted, and there will be no problem of blindly adding the reducing agent to generate a large amount of divalent iron ions and increase the pressure of the iron and aluminum removal process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 A schematic diagram of a typical process flow for removing hexavalent chromium in a high-pressure acid leaching process of laterite nickel ore according to the present invention is shown;

[0020] Figure 2 The graph shows the relationship between the hexavalent chromium concentration and the potential of the reference solution when removing hexavalent chromium in the high-pressure acid leaching process of laterite nickel ore according to the present invention, tested at 80°C;

[0021] Figure 3 The graph shows the relationship between the hexavalent chromium concentration and the potential of the reference solution tested at 70° C. when removing hexavalent chromium in the high-pressure acid leaching process of laterite nickel ore according to the present invention. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] In order to solve the problems in the prior art as mentioned above, the present invention provides a method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore, such as Figure 1 As shown, the high-pressure acid leaching process of laterite nickel ore includes a high-pressure acid leaching step, a circulating leaching step, a neutralization step, a CCD countercurrent washing step, a first-stage iron and aluminum removal step, a second-stage iron and aluminum removal step, and a nickel and cobalt precipitation step, wherein:

[0024] After the CCD countercurrent washing step, a CCD overflow liquid is obtained; judging whether hexavalent chromium ions exist according to the b value of the LAB color mode of the CCD overflow liquid, and detecting the hexavalent chromium ion concentration in the CCD overflow liquid according to the potential value of the CCD overflow liquid; secondly, adding a reducing agent to the CCD overflow liquid, and then allowing the CCD overflow liquid with the added reducing agent to enter a first iron and aluminum removal step; wherein the amount of the reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the CCD overflow liquid are reduced to trivalent chromium ions, and does not exceed 1.5 times of the theoretical amount; optionally, after a stage of iron and aluminum removal step, a stage of iron and aluminum removal liquid is obtained, and whether hexavalent chromium ions are present is determined according to the b value of the LAB color mode of the stage of iron and aluminum removal liquid; if present, the concentration of hexavalent chromium ions therein is detected according to the potential value of the stage of iron and aluminum removal liquid, and a reducing agent is continuously added to the stage of iron and aluminum removal liquid; wherein the amount of the reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the stage of iron and aluminum removal liquid are reduced to trivalent chromium ions, and does not exceed 1.5 times of the theoretical amount.

[0025] The present invention provides a method for high-pressure acid leaching process that does not affect laterite nickel ore, while being able to achieve rapid detection, rapid reduction and removal of hexavalent chromium ions. It is known from the study of the high-pressure acid leaching process of laterite nickel ore in the prior art that if the neutralization step is typically performed using residual ore, the residual ore itself will produce a portion of divalent iron ions, and the divalent iron ions can reduce a portion of the hexavalent chromium ions. Therefore, the present invention selects to qualitatively and quantitatively test the hexavalent chromium content according to the b value and potential value of the LAB color model after the CCD countercurrent washing step, and then add a reducing agent to the obtained CCD overflow liquid, so that the hexavalent chromium can be removed using relatively less reducing agent. And after the CCD countercurrent washing, the chromium can be further removed in a further iron and aluminum removal step.

[0026] The inventors found that at a certain temperature (such as 70-80°C), and at a certain concentration of Ni ions, Fe ions, and Al ions (such as Ni ion concentration 2-9g / L, Fe ion concentration 0.3-7g / L, Al ion concentration 0.3-7g / L), there is a linear relationship between the concentration of hexavalent chromium ions in the CCD overflow liquid and the liquid after a section of iron and aluminum removal and the potential value (Ag / AgCl). Based on this, chromium removal can be performed more accurately through potential monitoring. This method has a fast test speed, conforms to the actual production environment, and can make the dosage of the reducing agent more accurate and the reduction efficiency higher. In addition, when the solution contains hexavalent chromium ions, the color is yellow; when the solution does not contain hexavalent chromium ions, the color is blue-green. It is difficult to distinguish subtle color differences with the naked eye, so it is judged by the LAB value. The b value of the LAB color mode can characterize the color change from blue to yellow, ranging from -128 to +128, pure blue is -128, pure yellow is +128, and there are 256 levels in between. When the b value shows a positive value, the solution turns yellow, which means that the CCD overflow contains hexavalent chromium ions. At this time, a reducing agent should be added to remove chromium. This method is simple and fast, does not require multiple sampling, and can alleviate the disadvantage of inconvenient analysis and testing of hexavalent chromium ion concentration under industrial and mining conditions.

[0027] The present invention can combine the potential value of the test CCD overflow liquid and the optional liquid after the iron and aluminum removal with the b value of the LAB color model, quickly and semi-quantitatively determine the concentration of hexavalent chromium, control the amount of reducing agent, and only need to add a reducing agent that is no more than 1.5 times the theoretical amount to achieve the purpose of removing hexavalent chromium ions. In the whole process, the dosage range of the reducing agent can be predicted, and there will be no problem of blindly adding reducing agents to produce a large amount of divalent iron ions and increase the pressure of the iron and aluminum removal process. After implementing the method of the present invention, the content of hexavalent chromium in the liquid phase system can reach less than 0.5 mg / L, and the Fe removal rate can also reach more than 98%.

[0028] In the present invention, the mechanism of reducing hexavalent chromium ions by the reducing agent includes the following processes: 1) the hexavalent chromium ions in the CCD overflow liquid and a small amount of Fe 3+ Reduced by a reducing agent to produce Fe 2+ Cr 3+ ; 2) Cr 3+ Converted into Cr(OH)3 or Cr(OH)3·nH2O and enter into the iron-aluminum slag.

[0029] In a preferred embodiment, the step of detecting the hexavalent chromium ion concentration in the CCD overflow liquid or the liquid after the iron and aluminum removal according to the potential value comprises: preparing reference solutions with different hexavalent chromium concentrations, and other cations in the reference solution other than hexavalent chromium are Ni ions, Fe 3+ Ions and Al 3+ions; test the Ag / AgCl potential of each reference solution and obtain the relationship curve between hexavalent chromium concentration and Ag / AgCl potential; use a potentiometer to test the Ag / AgCl potential of the CCD overflow liquid or the liquid after a section of iron and aluminum removal, and bring it into the relationship curve to obtain the hexavalent chromium ion concentration of the CCD overflow liquid or the liquid after a section of iron and aluminum removal. Ni ions, Fe 3+ Ions and Al 3+ The ions are typical cations in the CCD overflow liquid and the liquid after the first stage of iron and aluminum removal. Using a reference solution containing these ions can further improve the accuracy of the potential test curve. More preferably, the concentrations of other cations in the reference solution are: Ni ion 5g / L, Fe 2+ Ions 0.5~5g / L and Al 3+ Ions are 0.3 to 5 g / L, and its pH value is 4 to 5. In addition to cations, anions in the reference solution are preferably sulfate ions.

[0030] In order to make the potential test more accurate and thus further improve the accuracy of hexavalent chromium concentration measurement, in a preferred embodiment, during the process of detecting the Ag / AgCl potential of the standard solution, the temperature of the standard solution is maintained at the same temperature as the CCD countercurrent washing temperature; preferably, the temperature of the standard solution is maintained at 70-80°C.

[0031] In a preferred embodiment, the step of judging whether hexavalent chromium ions exist according to the b value of the LAB color mode of the CCD overflow liquid or the liquid after a section of iron and aluminum removal comprises: measuring the b value of the CCD overflow liquid or the liquid after a section of iron and aluminum removal in the LAB color mode by a colorimeter, wherein when the b value is a positive number, it indicates the presence of hexavalent chromium ions, and the larger the b value, the higher the concentration of hexavalent chromium ions. The b value of the LAB color mode can characterize the color change from blue to yellow, ranging from -128 to +128, pure blue is -128, pure yellow is +128, and there are 256 levels in between. When the b value shows a positive value, the solution turns yellow, which means that the CCD overflow liquid contains hexavalent chromium ions. According to this value, the approximate concentration of hexavalent chromium can be known in advance, and the subsequent combined potential test is more accurate and convenient.

[0032] In order to better avoid the adverse effects of excessive use of reducing agent, in a preferred embodiment, the amount of reducing agent added is 1 to 1.3 times the theoretical amount of reducing hexavalent chromium ions in the CCD overflow liquid to trivalent chromium ions. When the amount of reducing agent added exceeds the above preferred range, more trivalent iron ions will be reduced to divalent iron ions. Divalent iron ions are more difficult to remove than trivalent iron ions, which will increase the pressure of subsequent iron removal, and the excessive content of divalent iron ions will increase the corrosiveness of the equipment. It should be noted that it is precisely because the present invention adopts a simple, fast and semi-quantitative method of monitoring the potential value and / or testing the b value of the LAB color mode to determine the content of hexavalent chromium ions in the system that it can provide a basis for accurately controlling the amount of reducing agent.

[0033] For the purpose of better controlling the reaction process of reducing hexavalent chromium ions, in a preferred embodiment, the reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, sodium thiosulfate, sulfur, and sodium sulfide; preferably, the reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, and sodium thiosulfate. The above-mentioned reducing agents can better achieve the function of reducing hexavalent chromium. Sodium sulfite, sodium pyrosulfite, ferrous sulfate, and sodium thiosulfate are more preferred reducing agents because the actual amount of these reducing agents is basically consistent with the theoretical amount of reducing hexavalent chromium, and the reaction speed is fast, and the reaction can usually be completed within 15 minutes, which is conducive to timely sampling and measurement, thereby better realizing the technical solution of rapid detection and accurate addition of reducing agents. However, sulfur or sodium sulfide is less effective in the system of the CCD overflow liquid stage.

[0034] In a preferred embodiment, the iron and aluminum removal step includes a first-stage iron and aluminum removal step and a second-stage iron and aluminum removal step performed sequentially; after the first-stage iron and aluminum removal step, a first-stage iron and aluminum removal liquid is obtained; after the second-stage iron and aluminum removal step, a second-stage iron and aluminum removal liquid is obtained. Carrying out the two-stage iron and aluminum removal process sequentially is more conducive to the removal of iron and aluminum. In the previous CCD countercurrent washing step, hexavalent chromium ions are reduced to trivalent chromium precipitates, which can enter the ferroaluminum slag. Even if a small amount of hexavalent chromium ions have not been completely reduced in the aforementioned steps, they can also be removed in the first-stage iron and aluminum removal step; if there are still hexavalent chromium ions in the first-stage iron and aluminum removal liquid, continue to remove them in the second-stage iron and aluminum removal step (in the actual production process, this process is generally not required to be implemented).

[0035] In a preferred embodiment, the one-stage iron and aluminum removal step includes: adjusting the pH value of the CCD overflow liquid to which the reducing agent is added to 2.0-5.0, introducing an oxygen-containing gas (such as air, oxygen), and then reacting at 55-90°C for 10 minutes to 20 hours; after the one-stage iron and aluminum removal step, a one-stage iron and aluminum removal liquid is obtained. Such preferred conditions are more conducive to fully removing iron and aluminum. Because the amount of reducing agent added in the pre-step is relatively small, in the present invention, the pressure of the one-stage iron and aluminum removal process is relatively small.

[0036] In a preferred embodiment, the second stage iron and aluminum removal step includes: introducing oxygen-containing gas into the liquid after the first stage iron and aluminum removal, adjusting the pH value to 4.0-6.0, and then reacting at 45-80° C. for 10 min-20 h. Such preferred conditions are more conducive to fully removing iron and aluminum.

[0037] In a preferred embodiment, in the first iron and aluminum removal step and the second iron and aluminum removal step, one or more of calcium carbonate, sodium hydroxide, calcium hydroxide, and calcium oxide are used as pH regulators independently; preferably, the oxygen-containing gas is air or oxygen. Such preferred conditions are more conducive to fully removing iron and aluminum.

[0038] When it is necessary to reduce hexavalent chromium ions in the step of two-stage aluminum removal, in a preferred embodiment, the method further comprises: adding a reducing agent in the process of two-stage aluminum removal, and the amount of the added reducing agent is 1 to 1.5 times the theoretical amount when the hexavalent chromium ions in the liquid after the two-stage aluminum removal are reduced to trivalent chromium ions. The above preferred amount of reducing agent is more conducive to the full reduction of hexavalent chromium ions in this process. If the amount of reducing agent is too much, the trivalent iron ions will be reduced to produce more divalent iron ions. The divalent iron ions need to be oxidized to trivalent iron ions under aerobic conditions, and then converted into iron hydroxide precipitation. There are more divalent iron ions, which need to consume more oxygen, and the iron removal effect is also affected. In addition, the reducing agent is also wasted.

[0039] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0040] The relationship curve test between hexavalent chromium concentration and Ag / AgCl potential:

[0041] At 80°C, reference solutions with ion concentrations of Ni: 5g / L, Fe: 5g / L, Al: 4g / L and pH 5 were prepared. The relationship between the hexavalent chromium concentration and the reference solution potential (Ag / AgCl) was tested by a potentiometer. Figure 2 shown.

[0042] At 70°C, reference solutions with ion concentrations of Ni: 5g / L, Fe: 0.5g / L, Al: 0.3g / L and pH 4 were prepared. The relationship between the hexavalent chromium concentration and the reference solution potential (Ag / AgCl) was tested by a potentiometer. Figure 3 shown.

[0043] Example 1

[0044] Taking a laterite nickel mine as the implementation object, the Ni ion concentration in the CCD overflow liquid is 6g / L, the Fe ion concentration is 4g / L, and the Al ion concentration is 5g / L. The solution is yellow and the LAB color mode b value is positive, indicating that there is hexavalent chromium in the solution. Secondly, by testing the CCD overflow liquid potential at 80°C, it is 939mv. Substituting it into the above hexavalent chromium concentration and potential (Ag / AgCl) corresponding relationship curve, it is concluded that the hexavalent chromium ion concentration is 387mg / L (the chemical precipitation method actually measured 404mg / L, proving that the test is more effective).

[0045] According to the hexavalent chromium ion concentration in 1L CCD overflow liquid, Cr2O7 2- The absolute mass is 387 mg. The reducing agent is as follows:

[0046] The mass ratio of sodium sulfite to sodium metabisulfite is 1:1. The molecular weight of sodium sulfite is 126.04 g / mol, and the molecular weight of sodium metabisulfite Na2S2O5 is 190.10. Theoretically, 387 mg Cr2O7 is reduced. 2- The theoretically required masses of sodium sulfite and sodium metabisulfite are 112.91 mg and 170.30 mg respectively. At 1.1 times, the consumption of the two agents is 124.20 mg and 187.33 mg respectively.

[0047] Sodium sulfite reduction mechanism:

[0048] SO3 2- +H + +Cr2O7 2- →SO4 2- +H2O+Cr 3+

[0049] Sodium metabisulfite reduction mechanism:

[0050] Cr2O7 2- +1.5S2O5 2- +5H + =3SO4 2- +2Cr 3+ +2.5H2O

[0051] Sodium metabisulfite and sodium sulfite, 1.1 times the theoretical amount of hexavalent chromium to be completely reduced, were added to the CCD overflow liquid, with a mass ratio of 1:1. The CCD overflow liquid with the addition of the reducing agent entered a step of iron and aluminum removal, and the pH of the overflow liquid was adjusted to 3.8 with calcium carbonate slurry, the reaction temperature was 75°C, and the reaction time was 6h. After the reaction, the hexavalent chromium concentration in the CCD overflow liquid was less than 0.5 mg / L, the total iron concentration was 900 mg / L, the divalent iron ion concentration was 32 mg / L, the solution was blue-green, the LAB color mode b value was negative, and the potential was further tested at 80°C to be 597 mv. The result shows that the hexavalent chromium in the system has been basically removed, and the measured hexavalent chromium concentration in the CCD overflow liquid is less than 0.5 mg / L, indicating that the hexavalent chromium has been completely removed.

[0052] Example 2

[0053] The difference from Example 1 is that 1.25 times the theoretical amount of sodium metabisulfite and sodium thiosulfate for completely reducing hexavalent chromium is added to the CCD overflow liquid, and the mass ratio of the two is 1:10. After chromium removal, the solution is blue and the potential is 527mv. This result shows that the hexavalent chromium in the system has been basically removed. The measured hexavalent chromium concentration in the CCD overflow liquid is less than 0.5mg / L, which further shows that the hexavalent chromium is completely removed.

[0054] Example 3

[0055] The potential of the CCD overflow liquid is 851mv. Substituting it into the above-mentioned hexavalent chromium concentration and potential (Ag / AgCl) corresponding relationship curve, the corresponding hexavalent chromium ion concentration is obtained to be 201mg / L (the hexavalent chromium concentration measured by chemical precipitation method is 217mg / L).

[0056] Before the first iron and aluminum removal process, sodium metabisulfite and sodium sulfite, which are 1.1 times the theoretical amount of hexavalent chromium to be completely reduced, are added to the CCD overflow liquid, and the mass ratio of the two is 1:1. The CCD overflow liquid with the addition of the reducing agent enters the first iron and aluminum removal step, and the pH of the overflow liquid is adjusted to 3.9 with calcium carbonate slurry, the reaction temperature is 75°C, and the reaction time is 6h. After the reaction, the solution is blue-green, the LAB color mode b value is negative, and the potential is 534mv. This result shows that the hexavalent chromium in the system has been basically removed. The measured hexavalent chromium concentration in the CCD overflow liquid is less than 0.5mg / L, which further indicates that the hexavalent chromium has been completely removed.

[0057] Example 4

[0058] The only difference from Example 1 is that 1.1 times the theoretical amount of ferrous sulfate for completely reducing hexavalent chromium is added. After the reaction is completed, the solution is blue-green, the LAB color mode b value is negative, and the potential is 541mv. This result shows that the hexavalent chromium in the system has been basically removed. The measured hexavalent chromium concentration in the CCD overflow liquid is less than 0.5mg / L, which further indicates that the hexavalent chromium has been completely removed.

[0059] Example 5

[0060] The difference from Example 1 is that 1.5 times the theoretical amount of sodium metabisulfite and sodium sulfite required for completely reducing hexavalent chromium are added, and the mass ratio of the two is 1:1.

[0061] After the reaction, the solution was blue-green, the LAB color mode b value was negative, and the potential was 492mv, which showed that the hexavalent chromium had been completely removed. The measured hexavalent chromium concentration in the CCD overflow liquid was less than 0.5mg / L, indicating that the hexavalent chromium was completely removed.

[0062] Example 6

[0063] The difference from Example 1 is that the reaction temperature is adjusted to 90° C., the reaction time is 20 min, and pure oxygen is introduced.

[0064] After the reaction, the solution was blue-green, the LAB color mode b value was negative, and the potential was 502mv, indicating that the hexavalent chromium had been completely removed. The measured hexavalent chromium concentration in the CCD overflow liquid was less than 0.5mg / L, further indicating that the hexavalent chromium was completely removed.

[0065] Example 7

[0066] The difference from Example 1 is that in the first iron and aluminum removal step, the pH is adjusted to 2.0, pure oxygen is introduced, and the reaction is carried out for 7.5 hours.

[0067] After the reaction, the solution was blue-green, the LAB color mode b value was negative, and the potential was 534mv, indicating that the hexavalent chromium had been completely removed. The measured hexavalent chromium concentration in the CCD overflow liquid was less than 0.5mg / L, indicating that the hexavalent chromium was completely removed and this method was effective.

[0068] Example 8

[0069] The difference from Example 1 is that in the first iron and aluminum removal step, the pH is adjusted to 3.5, pure oxygen is introduced, and the reaction is carried out for 5 hours. Sodium sulfite is added, and the amount of sodium sulfite is 1 times the theoretical reduction amount.

[0070] After the reaction, the solution was blue-green, the LAB color mode b value was positive, and the potential was 660mv. According to the correspondence between the hexavalent chromium concentration and the potential (Ag / AgCl) in the typical iron and aluminum removal solution, the hexavalent chromium concentration was estimated to be 50mg / L. The measured hexavalent chromium concentration in the CCD overflow was 32mg / L. According to the estimated hexavalent chromium concentration of 50mg / L, 1.5 times of sodium sulfite was added during the second stage of iron and aluminum removal. After the reaction, the LAB color mode b value was negative, and the potential was 594mv. The results showed that the hexavalent chromium had been completely removed. The measured hexavalent chromium concentration in the CCD overflow was lower than 0.5mg / L, indicating that the hexavalent chromium was completely removed and this method was effective.

[0071] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0072] The present invention provides a method for rapidly detecting and rapidly reducing hexavalent chromium ions in a high-pressure acid leaching process of laterite nickel ore, and the amount of the reducing agent used is relatively accurate, which has less pressure on the subsequent iron and aluminum removal process and has good industrial value.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for removing hexavalent chromium in a high-pressure acid leaching process for laterite nickel ore, the high-pressure acid leaching process for laterite nickel ore comprising a high-pressure acid leaching step, a circulating leaching step, a neutralization step, a CCD countercurrent washing step, a first-stage iron and aluminum removal step, a second-stage iron and aluminum removal step, and a nickel and cobalt precipitation step performed in sequence, characterized in that: After the CCD countercurrent washing step, a CCD overflow liquid is obtained; judging whether hexavalent chromium ions exist according to the b value of the LAB color mode of the CCD overflow liquid, and detecting the hexavalent chromium ion concentration in the CCD overflow liquid according to the potential value of the CCD overflow liquid; secondly, adding a reducing agent to the CCD overflow liquid, and then allowing the CCD overflow liquid with the reducing agent added to enter the first iron and aluminum removal step; wherein the amount of the reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the CCD overflow liquid are reduced to trivalent chromium ions, and does not exceed 1.5 times the theoretical amount; Optionally, after the one-stage iron and aluminum removal step, a stage of iron and aluminum removal liquid is obtained, and whether hexavalent chromium ions exist is determined according to the b value of the LAB color mode of the one-stage iron and aluminum removal liquid. If so, the concentration of hexavalent chromium ions therein is detected according to the potential value of the one-stage iron and aluminum removal liquid, and the reducing agent is continuously added to the one-stage iron and aluminum removal liquid; wherein the amount of the reducing agent added is greater than or equal to the theoretical amount when the hexavalent chromium ions in the one-stage iron and aluminum removal liquid are reduced to trivalent chromium ions, and is not more than 1.5 times the theoretical amount.

2. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 1, characterized in that: The step of detecting the hexavalent chromium ion concentration in the CCD overflow liquid or the liquid after the first stage of iron and aluminum removal according to the potential value comprises: Reference solutions with different hexavalent chromium concentrations were prepared, and other cations in the reference solutions besides hexavalent chromium were Ni ions, Fe 3+ Ions and Al 3+ ion; Testing the Ag / AgCl potential of each of the reference solutions, and obtaining a relationship curve between the hexavalent chromium concentration and the Ag / AgCl potential; The Ag / AgCl potential of the CCD overflow liquid or the liquid after the first stage of iron and aluminum removal is tested by a potentiometer, and is brought into the relationship curve to obtain the hexavalent chromium ion concentration of the CCD overflow liquid or the liquid after the first stage of iron and aluminum removal.

3. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 2, characterized in that: The concentrations of other cations in the reference solution are: Ni ion 5g / L, Fe 2+ Ions 0.5~5g / L and Al 3+ Ions are 0.3-4 g / L, and its pH value is 4-5.

4. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 2, characterized in that: During the process of detecting the Ag / AgCl potential of the standard solution, the temperature of the standard solution is maintained to be the same as the temperature of the CCD countercurrent washing; preferably, the temperature of the standard solution is maintained at 70-80°C.

5. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 1, characterized in that: The step of judging whether hexavalent chromium ions exist according to the b value of the LAB color mode of the CCD overflow liquid or the liquid after the iron and aluminum removal comprises: The b value of the CCD overflow liquid or the liquid after the first stage of iron and aluminum removal in the LAB color mode is measured by a colorimeter, wherein when the b value is a positive number, it indicates the presence of hexavalent chromium ions, and the larger the b value, the higher the concentration of hexavalent chromium ions.

6. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to any one of claims 1 to 5, characterized in that: The amount of the reducing agent added is 1 to 1.3 times the theoretical amount for reducing the hexavalent chromium ions in the CCD overflow liquid to trivalent chromium ions.

7. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to any one of claims 1 to 5, characterized in that: The reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, sodium thiosulfate, sulfur, and sodium sulfide; preferably, the reducing agent includes one or more of sodium sulfite, sodium pyrosulfite, ferrous sulfate, and sodium thiosulfate.

8. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 7, characterized in that: The one-stage iron and aluminum removal step comprises: adjusting the pH value of the CCD overflow liquid to which the reducing agent is added to 2.0-5.0, introducing oxygen-containing gas, and then reacting at 55-90° C. for 10 minutes to 20 hours.

9. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 7, characterized in that: The second stage iron and aluminum removal step comprises: introducing oxygen-containing gas into the reaction solution obtained in the first stage iron and aluminum removal step, adjusting the pH value to 4.0-6.0, and then reacting at 45-80° C. for 10 minutes to 20 hours.

10. The method for removing hexavalent chromium in a high pressure acid leaching process of laterite nickel ore according to claim 7, characterized in that: In the first stage of iron removal and the second stage of iron removal, each independently: Using one or more of calcium carbonate, sodium hydroxide, calcium hydroxide, and calcium oxide as a pH regulator; Preferably, the oxygen-containing gas is air or oxygen.

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