Method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater

Abstract

The application belongs to the technical field of hydrometallurgy, and particularly relates to a method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater, which comprises the following steps: (1) adding oxalic acid into nickel-cobalt precipitation wastewater containing calcium and manganese; (2) adding a crystal seed inducer to obtain calcium slag and purified liquid; (3) reacting the calcium slag in step (2) with sulfuric acid, and filtering the calcium sulfate slag and oxalic acid mother liquor while hot; and (4) cooling the oxalic acid mother liquor in step (3) to precipitate oxalic acid crystals, and filtering the oxalic acid and crystallization mother liquor. The application constructs a complete oxalic acid closed-circuit system; the calcium oxalate slag generated in the calcium removal process is converted by sulfuric acid, and the generated oxalic acid solution can be recovered by cooling crystallization, the mother liquor is supplemented with sulfuric acid and water and then recycled for leaching, and the recovered oxalic acid crystals are returned to the calcium removal process; the design greatly reduces the consumption of oxalic acid, a main consumable, and significantly reduces the production cost.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for recovering magnesium from wastewater containing calcium and manganese in laterite nickel ore smelting. Background Technology

[0002] The nickel-cobalt precipitation waste liquid generated during the hydrometallurgical process of laterite nickel ore typically contains a high concentration of Mg of about 12 g / L. 2+ 0.6 g / L of Ca 2+ and 3g / L of Mn 2+ This waste liquid has high resource recovery value. Industrially, a process combining evaporation and concentration with cooling crystallization or pyrolysis spray drying is commonly used to prepare magnesium sulfate crystals from this waste liquid. However, during the evaporation and concentration stage, the Ca in the waste liquid... 2+ As the concentration increases, the solution tends to become saturated, leading to the precipitation of calcium sulfate (CaSO4) scale, which can cause scaling and even blockage in evaporation equipment. Therefore, effective calcium removal pretreatment of the waste liquid is necessary before recovering magnesium sulfate.

[0003] Currently, the most commonly used industrial method for calcium removal is chemical precipitation, with common precipitants including fluorides, carbonates, phosphates, and oxalic acid. While these methods can achieve good calcium removal results, they each have significant drawbacks: fluoride precipitation is highly corrosive and easily causes environmental pollution; carbonate and phosphate methods tend to induce co-precipitation of magnesium and calcium ions, leading to a significant decrease in magnesium recovery. In contrast, oxalic acid precipitation is less effective because calcium oxalate (CaC₂O₄) has an extremely low solubility product (Ksp≈2.6×10⁻⁶). -9 ), can selectively add Ca 2+ The precipitate is calcium oxalate, while Mg... 2+ and Mn 2+ This process produces virtually no precipitation, giving it a significant advantage. Furthermore, the resulting calcium oxalate slag can be converted into calcium sulfate (which can be sold as gypsum) and oxalic acid through sulfuric acid leaching, achieving the regeneration and reuse of oxalic acid. This "oxalic acid precipitation – calcium slag conversion" process boasts advantages such as low cost, high calcium removal efficiency, and safety and environmental friendliness, demonstrating promising application prospects.

[0004] In the prior art, patent CN109516628A discloses a method for extracting magnesium sulfate from high-magnesium, low-calcium power plant wastewater, using oxalic acid as a calcium removal agent. 2+ The removal rate can reach over 95%, but there are drawbacks such as high oxalic acid dosage and Mg content. 2+ The problem involves a loss rate of up to 3%. Patent CN119370872A discloses a resource-based treatment process for magnesium-manganese ammonium sulfate wastewater. This process promotes calcium precipitation of oxalic acid by adding a seed crystal inducer and employs ozone catalytic oxidation to remove Mg... 2+ The Mg was removed by oxidation to MnO2 precipitate, but this document describes the process at high concentrations of Mg. 2+Under coexisting conditions, it is difficult to achieve Ca2+ by simply adding oxalic acid according to the stoichiometric ratio. 2+ Efficient removal often requires a large overdose, leading to high oxalic acid consumption and operating costs; the reaction of excess oxalic acid with Mg as the concentration increases during subsequent evaporation and concentration is not adequately considered. 2+ The risk of magnesium oxalate (MgC2O4) precipitation may arise, potentially leading to equipment scaling or product contamination; this also applies to Mn in high-magnesium wastewater. 2+ Existing methods for removing [the pollutants] rely on strong oxidants such as ozone, which are costly and increase process complexity and operational burden.

[0005] Therefore, there is an urgent need to develop an integrated process that can efficiently remove calcium, prevent magnesium oxalate precipitation, remove manganese ions at low cost, and realize the recycling of oxalic acid, so as to solve the above-mentioned technical bottlenecks and improve the economic efficiency and sustainability of magnesium resource recovery from laterite nickel ore smelting waste liquid. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater. This method utilizes crystal-induced precipitation and crystallization impurity removal technologies to achieve efficient removal of calcium ions, efficient conversion of calcium slag, and efficient removal of manganese ions from high-magnesium nickel cobalt precipitated wastewater. At the same time, it ensures that no magnesium salts precipitate during the evaporation and concentration process of the purified liquid. This method has simple procedures, low cost, and is conducive to industrial production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater includes the following steps: (1) Add oxalic acid to the nickel-cobalt precipitate containing calcium and manganese, and stir to fully dissolve the oxalic acid. The amount of oxalic acid added is 2-6.4 g / L. (2) Add seed crystal inducer and react at room temperature for a period of time. After the reaction is completed, filter to obtain calcium slag and purified liquid; (3) React the calcium slag in step (2) with sulfuric acid at a certain temperature for a period of time, and filter while hot to obtain calcium sulfate slag and oxalic acid mother liquor; (4) Cool the oxalic acid mother liquor in step (3) until oxalic acid crystals precipitate, filter to obtain oxalic acid and crystallization mother liquor, add a certain amount of water and sulfuric acid to the crystallization mother liquor and return it to step (3) for recycling, and return the oxalic acid to step (1) for recycling; (5) The purified liquid in step (2) is concentrated by evaporation and cooled to crystallize, resulting in magnesium sulfate crystals and manganese-containing mother liquor.

[0008] In step (1), the Mg in the nickel-cobalt precipitated waste liquid 2+ The concentration is 12-15 g / L, Ca 2+The concentration is 0.6-0.8 g / L, Mn 2+ The concentration is 1.5-3.0 g / L, and the pH is 8.5-8.8.

[0009] Before adding the oxalic acid, the nickel-cobalt precipitate waste liquid is pretreated, that is, the pH of the solution is adjusted to 2-9 with liquid alkali.

[0010] The amount of oxalic acid added is 2-4 g / L.

[0011] The seed inducer in step (2) includes one or more combinations of calcium carbonate, magnesium carbonate, manganese carbonate, calcium oxalate, magnesium oxalate, manganese oxalate, and calcium sulfate.

[0012] The amount of the seed crystal inducer added is 1-30 wt% of the solution mass; the temperature of the calcium removal reaction is set at 20℃-25℃, and the reaction time is set at 10-120 min.

[0013] In step (3), the calcium slag conversion temperature is controlled at 30-90℃, the sulfuric acid concentration is controlled at 5-98%, the amount of sulfuric acid is controlled at 1-4 times the molar amount of calcium in the calcium slag, and the reaction time is controlled at 0.5-2h.

[0014] The cooling temperature of the oxalic acid mother liquor is controlled between 0-30℃.

[0015] In step (5), during the evaporation and concentration process, the evaporation and concentration are stopped after the solution volume is reduced to 5-15% of the original solution; and the temperature of the concentrated liquid for cooling and crystallization is controlled at 0-30℃.

[0016] The beneficial effects of this invention are as follows: (1) Due to the presence of a large amount of Mg in the solution 2+ , while Mg 2+ Ca 2+ and C2O4 2- The coordination constants are similar, especially at high concentrations of Mg. 2+ C2O4 under the conditions 2- Prefers Mg 2+ Coordination. Therefore, when the actual amount of oxalate used is much greater than the theoretical amount required for oxalate to bind with calcium ions (i.e., the molar ratio is 1), Ca... 2+ Only then can complete precipitation occur; and by introducing seed crystals, the nucleation sites of calcium oxalate in the solution can be increased, promoting Ca... 2+ With C2O4 2-The calcium oxalate is formed by combining with the calcium oxalate, thereby reducing the amount of oxalic acid used. Therefore, this application strictly limits the amount of oxalic acid to 1.0 to 3.2 times the theoretical amount (2-6.4 g / L). While ensuring the effective removal of calcium ions, it cleverly avoids the problem of magnesium oxalate (MgC2O4) precipitation in the subsequent evaporation and concentration process due to excessive oxalic acid. This optimization balances the calcium removal efficiency and system stability, solves the bottleneck of evaporator blockage due to magnesium oxalate or calcium sulfate precipitation, and ensures the continuous and stable operation of the entire recovery process. (2) This application abandons the complicated method of relying on expensive oxidants (such as ozone, hydrogen peroxide, etc.) to oxidize and precipitate manganese ions in the traditional process. Instead, it makes full use of the significant difference in solubility between magnesium sulfate and manganese sulfate at different temperatures. By controlling the evaporation concentration ratio and cooling crystallization temperature, magnesium sulfate is preferentially crystallized out, while manganese salt is enriched in the mother liquor and thus separated. This method does not require the addition of any manganese removal reagents, which not only greatly reduces reagent costs and operational complexity, but also avoids the introduction of new impurity ions. It is a green, efficient and economical manganese removal strategy. (3) This application constructs a complete closed-loop recycling system for oxalic acid; after the calcium oxalate residue produced in the calcium removal process is converted by sulfuric acid, the oxalic acid solution generated can be recovered by cooling and crystallization, the mother liquor is replenished with sulfuric acid and water and then recycled for leaching, and the recovered oxalic acid crystals are returned to the calcium removal process; this design greatly reduces the amount of oxalic acid, the main consumable, and significantly reduces production costs. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] like Figure 1 As shown, a method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater includes the following steps: (1) Add oxalic acid to the nickel-cobalt precipitated waste liquid containing calcium and manganese (or nickel-cobalt precipitated waste liquid) and stir to fully dissolve the oxalic acid; Among them, Mg in nickel-cobalt precipitated waste liquid 2+ The concentration is 12-15 g / L, Ca 2+ The concentration is 0.6-0.8 g / L, Mn 2+ The concentration is 1.5-3.0 g / L, and the pH is 8.5-8.8; Before adding oxalic acid, the nickel-cobalt precipitate waste liquid is pretreated by adjusting the pH of the solution to 2-9 with liquid alkali, generally controlled at 5-7; the amount of oxalic acid added is 2-6.4 g / L, generally controlled at 2-4 g / L. (2) Add seed crystal inducer and react at 20℃-25℃ for 10-120 min. After the reaction is completed, filter to obtain calcium slag and purified liquid. The seed crystal inducer includes one or more combinations of calcium carbonate, magnesium carbonate, manganese carbonate, calcium oxalate, magnesium oxalate, manganese oxalate, and calcium sulfate; the amount of seed crystal inducer added is 1-30 wt% of the solution mass, generally controlled at 1-20 wt%. (3) React the calcium slag in step (2) with sulfuric acid at a certain temperature for a period of time, and filter while hot to obtain calcium sulfate slag and oxalic acid mother liquor; The conversion temperature of calcium slag is controlled at 30-90℃, generally at 60-90℃; the sulfuric acid concentration is controlled at 5-98%, generally at 30-98%; the amount of sulfuric acid is controlled at 1-4 times the molar amount of calcium in the calcium slag; and the reaction time is controlled at 0.5-2h. Generally, the amount of sulfuric acid is controlled at 1-3 times the molar amount of calcium in the calcium slag; and the reaction time should be controlled at 1-1.5h. (4) Cool the oxalic acid mother liquor in step (3) until oxalic acid crystals precipitate. The cooling temperature of the oxalic acid mother liquor is controlled at 0-30℃. Then filter to obtain oxalic acid and crystal mother liquor. Add a certain amount of water and sulfuric acid to the crystal mother liquor to make its acidity consistent with the sulfuric acid concentration in step (3). Then return to step (3) for recycling. Oxalic acid is returned to step (1) for recycling. (5) The purified liquid in step (2) is evaporated, concentrated and cooled to crystallize to obtain magnesium sulfate crystals and manganese-containing mother liquor; wherein, after the solution volume is reduced to 5-15% of the original solution, generally reduced to 12.5-15% of the original solution, the evaporation and concentration are stopped; and the temperature of the concentrated liquid is controlled at 0-30℃ for cooling and crystallization.

[0020] The reaction equation for oxalic acid and calcium sulfate is: CaSO4 + H2C2O4 ⇌ CaC2O4 + H2SO4. The acidification reaction of calcium oxalate is a reversible, heterogeneous reaction. The solubility product of calcium oxalate is 2.6 × 10⁻⁶. -9 The solubility product of calcium sulfate is 6.1 × 10⁻⁶. -5 Because the reactants are less soluble than the products, such a reaction is difficult to carry out; however, since the reactants are strong acids and oxalic acid is a weak acid, the acidification reaction can proceed. Magnesium sulfate and manganese sulfate have significantly different solubilities. At 10℃, the solubility of manganese sulfate is 536 g / L, while the solubility of magnesium sulfate is 308 g / L, and the temperature dependence of magnesium sulfate solubility is stronger than that of manganese sulfate. Therefore, under high magnesium concentration conditions, by strictly controlling the concentration ratio during evaporation, concentration, and cooling crystallization, manganese sulfate will not precipitate, thus achieving manganese removal.

[0021] If too much oxalic acid is added, the residual oxalic acid concentration will gradually increase during crystallization, combining with high-concentration magnesium ions to form magnesium oxalate precipitation. If too little oxalic acid is added, residual calcium ions will reach saturation, precipitating and clogging the evaporator. Therefore, precise control of the amount of oxalic acid added is crucial to balance the calcium content. 2+ SO4 2- and C2O4 2- This results in no calcium or magnesium salts precipitating during the evaporation and concentration process.

[0022] Therefore, the technical solution of this application, based on seed-induced precipitation and crystallization impurity removal process, removes calcium and manganese from laterite nickel ore smelting wastewater and recovers magnesium sulfate. Compared with similar preparation processes in the prior art, it has the following significant advantages: The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater disclosed in this application has the advantage of employing a closed-loop process of oxalic acid regeneration and recycling, which significantly reduces the amount and cost of oxalic acid precipitant; by precisely controlling the amount of oxalic acid added, the Ca content during the evaporation process is reduced. 2+ SO4 2- and C2O4 2- To reach equilibrium without precipitation, i.e., Ca 2+ No deep removal is required, further reducing the amount of oxalic acid precipitant needed and saving costs. Furthermore, the crystallization manganese removal process disclosed in this application requires no other reagents; high impurity removal efficiency can be achieved simply by controlling process parameters such as the concentration ratio and cooling temperature. It features simple process, low cost, and is environmentally friendly and pollution-free. Example 1

[0023] A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater includes the following steps: (1) Mg in nickel-cobalt precipitated waste liquid 2+ It is 13.73 g / L, Ca 2+ The concentration of Mn is 0.64 g / L. 2+ The concentration was 3.15 g / L, the pH was controlled at 8.6, 5.3 g / L of oxalic acid was added and stirred to dissolve it completely, and the pH was adjusted to 6.0 with liquid alkali; (2) Add 1.5wt% calcium oxalate as a seed crystal inducer, react at 30℃ for 1h, filter to obtain calcium slag and purified liquid, and measure the residual Ca in the solution. 2+ The concentration is 0.06 g / L, Ca 2+ The removal rate was 90.63%, Mg 2+ and Mn 2+ No sedimentation; (3) Calcium slag was reacted with 30wt% dilute sulfuric acid, the amount of sulfuric acid being twice the molar amount of calcium in the calcium slag, at 70 °C for 1 h. The mixture was filtered while hot to obtain calcium sulfate slag and oxalic acid solution. The conversion rate of oxalic acid was measured to be 94.9%. (4) Cool the oxalic acid solution to 20°C to precipitate oxalic acid crystals. Filter to obtain a mixture of oxalic acid and sulfuric acid-oxalic acid. Add a certain amount of water and sulfuric acid to the mixture and then recycle it. The oxalic acid is returned to step (1). (5) The purified liquid was evaporated and concentrated to 12.5% ​​of the original volume, cooled to 10 °C, and the solution was crystallized to obtain magnesium sulfate crystals and manganese-containing mother liquor. The removal rate of manganese was measured to be 98.32%, and the manganese content in magnesium sulfate was <1%.

[0024] Comparative Example 1 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that "the addition of oxalic acid in step (1) was changed from 5.3 g / L to 3 g / L", while other conditions remained unchanged. The residual Ca in the solution was measured. 2+ The concentration is 0.1 g / L, Ca 2+ The removal rate was 84.38%, Mg 2+ and Mn 2+ No precipitation. Ca in Comparative Example 1 2+ The sharp decrease in removal rate is due to the reduced amount of oxalic acid used, which is insufficient to remove Ca. 2+ Precipitation from solutions with high concentrations of magnesium ions.

[0025] Comparative Example 2 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that "the addition of oxalic acid in step (1) was changed from 5.3 g / L to 8 g / L", while other conditions remained unchanged. The residual Ca in the solution was measured. 2+ The concentration is 0.03 g / L, Ca 2+ The removal rate was 92.18%, Mg 2+ and Mn 2+ The precipitation rates were 10.21% and 7.89%, respectively. (Comparative Example 2: Mg) 2+ and Mn 2+ The precipitation occurs because the concentration of oxalate is too high, which destroys the complexation state of oxalate with magnesium and manganese ions, thus causing a precipitation reaction.

[0026] Comparative Example 3 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that the step of adjusting the pH with liquid alkali in step (1) was removed, while other conditions remained unchanged. The residual Ca in the solution was measured. 2+ The concentration is 0.09 g / L, Ca 2+ The removal rate was 85.94%, Mg 2+ No precipitation, Mn 2+ The precipitation rate was 13.32%. (Comparative Example 3, Ca...) 2+ The removal rate decreased because high pH caused OH to be removed. - Competition with oxalate for Ca2+ (The Ksp of Ca(OH)2 is approximately 5.5 × 10⁻⁶) -6 (much greater than calcium oxalate); while Mn 2+ The precipitation is caused by excessively high pH, ​​which triggers a hydrolysis reaction.

[0027] Comparative Example 4 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that "the 1.5wt% in step (2) was changed to 0wt%", while other conditions remained unchanged. The residual Ca in the solution was measured. 2+ The concentration is 0.4 g / L, Ca 2+ The removal rate was 37.50%, Mg 2+ and Mn 2+ No precipitation. Ca in Comparative Example 4 2+ The removal rate drops sharply because seed crystals can increase nucleation sites and promote calcium oxalate precipitation.

[0028] Comparative Example 5 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that the reaction temperature in step (2) was changed from 30°C to 60°C, while other conditions remained the same. The residual Ca in the solution was measured. 2+ The concentration is 0.14 g / L, Ca 2+ The removal rate was 78.13%, Mg 2+ and Mn 2+ No precipitation. Ca in Comparative Example 5 2+ The removal rate drops sharply because the calcium precipitation reaction is an exothermic reaction, and calcium ions may dissolve back as the temperature rises.

[0029] Comparative Example 6 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that the reaction temperature in step (2) was changed from 1 h to 0.5 h, while other conditions remained the same. The residual Ca in the solution was measured. 2+ The concentration is 0.13 g / L, Ca 2+ The removal rate was 79.69%, Mg 2+ and Mn 2+ No precipitation. Ca in Comparative Example 6 2+ The removal rate dropped sharply because the reaction time was insufficient and the seed crystals did not induce the reaction sufficiently.

[0030] Comparative Example 7 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that the sulfuric acid concentration in step (3) was changed from 30 wt% to 98 wt%, while other conditions remained unchanged. The oxalic acid conversion rate was measured to be 36.2%. The oxalic acid conversion rate of Comparative Example 7 decreased sharply because the excessively high concentration led to an overly rapid acidification reaction kinetic, resulting in the in-situ formation of a dense calcium sulfate film on the surface of calcium oxalate, which terminated the reaction.

[0031] Comparative Example 8 A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater was repeated in Example 1, except that "12.5% ​​in step (5) was changed to 5%", while other conditions remained unchanged. The manganese removal rate was measured to be 69.90%. The manganese removal rate of Comparative Example 8 decreased sharply because the concentration factor was too large, which caused the manganese sulfate to approach saturation, and then entered the magnesium sulfate product during cooling and crystallization.

[0032] The method provided in this application achieves the goal of efficiently and stably removing calcium and manganese and recovering high-quality magnesium sulfate from laterite nickel ore smelting wastewater through a series of synergistically optimized process parameters.

[0033] The dosage of oxalic acid is a critical control point: Example 1, using 5.3 g / L of oxalic acid, achieved an excellent calcium removal rate of 90.63%. In contrast, Comparative Example 1 (3 g / L) suffered a calcium removal rate of only 84.38% due to insufficient dosage; while Comparative Example 2 (8 g / L), although achieving more thorough calcium removal, had the risk of magnesium oxalate precipitation during subsequent evaporation and concentration due to excessive oxalate. This demonstrates that the oxalic acid dosage range determined in this application represents a precise balance between ensuring effective calcium removal and preventing system scaling.

[0034] Process conditions need to be precisely controlled: pH value: Comparative Example 3 shows that not adjusting the pH (initial pH 8.6) not only reduces the calcium removal efficiency, but also leads to the hydrolysis and co-precipitation of manganese ions, affecting product purity.

[0035] Seed induction: Comparative example 4 confirmed that without the use of seed induction agent, the calcium removal rate dropped sharply to 37.50%, highlighting the key role of seed in promoting precipitation and reducing the amount of oxalic acid used.

[0036] Reaction conditions: Comparative Examples 5 and 6 show that excessively high reaction temperatures (60℃) or excessively short reaction times (0.5h) are not conducive to the full precipitation of calcium oxalate, resulting in a decrease in calcium removal efficiency.

[0037] Calcium slag conversion: Comparative Example 7 shows that using excessively high concentrations (98 wt%) of sulfuric acid for calcium slag conversion will significantly reduce the oxalic acid conversion rate to 36.2% due to the product encapsulation effect, thus affecting the recycling efficiency of oxalic acid.

[0038] Manganese removal by crystallization: Comparative example 8 shows that an excessively high evaporation concentration factor (up to 5%) will cause manganese sulfate to co-precipitate during crystallization, resulting in a decrease in the manganese removal rate from 98.32% to 69.90%, making it impossible to obtain magnesium sulfate products with low manganese content.

[0039] In summary, the technical solution of this application is not a simple change of a single parameter, but an organic whole in which each step and parameter is closely related and works synergistically. Only by following the process conditions defined in this application can high calcium removal rate, high manganese removal rate, high product purity, and long-term stable operation of the system be achieved simultaneously. Its technical effect is significantly better than that of comparative solutions where any single parameter deviates from the scope of this application.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments, or they can be used directly or indirectly, without departing from the principles and spirit of the invention. In other related technical fields, the scope of the invention is defined by the appended claims and their equivalents, and they are similarly included within the scope of patent protection of the invention.

Claims

1. A method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater, characterized in that, Includes the following steps: (1) Add oxalic acid to the nickel-cobalt precipitate containing calcium and manganese, and stir to fully dissolve the oxalic acid. The amount of oxalic acid added is 2-6.4 g / L. (2) Add seed crystal inducer and react at room temperature for a period of time. After the reaction is completed, filter to obtain calcium slag and purified liquid; (3) React the calcium slag in step (2) with sulfuric acid at a certain temperature for a period of time, and filter while hot to obtain calcium sulfate slag and oxalic acid mother liquor; (4) Cool the oxalic acid mother liquor in step (3) until oxalic acid crystals precipitate, filter to obtain oxalic acid and crystallization mother liquor, add a certain amount of water and sulfuric acid to the crystallization mother liquor and return it to step (3) for recycling, and return the oxalic acid to step (1) for recycling; (5) The purified liquid in step (2) is concentrated by evaporation and cooled to crystallize, resulting in magnesium sulfate crystals and manganese-containing mother liquor.

2. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 1, characterized in that: In step (1), the Mg in the nickel-cobalt precipitated waste liquid 2+ The concentration is 12-15 g / L, Ca 2+ The concentration is 0.6-0.8 g / L, Mn 2+ The concentration is 1.5-3.0 g / L, and the pH is 8.5-8.

8.

3. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 2, characterized in that: Before adding the oxalic acid, the nickel-cobalt precipitate waste liquid is pretreated, that is, the pH of the solution is adjusted to 2-9 with liquid alkali.

4. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 3, characterized in that: The amount of oxalic acid added is 2-4 g / L.

5. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 1, characterized in that: The seed inducer in step (2) includes one or more combinations of calcium carbonate, magnesium carbonate, manganese carbonate, calcium oxalate, magnesium oxalate, manganese oxalate, and calcium sulfate.

6. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 5, characterized in that: The amount of the seed crystal inducer added is 1-30 wt% of the solution mass; the temperature of the calcium removal reaction is set at 20℃-25℃, and the reaction time is set at 10-120 min.

7. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 1, characterized in that: In step (3), the calcium slag conversion temperature is controlled at 30-90℃, the sulfuric acid concentration is controlled at 5-98%, the amount of sulfuric acid is controlled at 1-4 times the molar amount of calcium in the calcium slag, and the reaction time is controlled at 0.5-2h.

8. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 1, characterized in that: The cooling temperature of the oxalic acid mother liquor is controlled between 0-30℃.

9. The method for removing calcium and manganese and recovering magnesium from laterite nickel ore smelting wastewater as described in claim 1, characterized in that: In step (5), during the evaporation and concentration process, the evaporation and concentration are stopped after the solution volume is reduced to 5-15% of the original solution; and the temperature of the concentrated liquid for cooling and crystallization is controlled at 0-30℃.

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