Method for producing high-purity nickel sulfate

Abstract

Provided is a method of producing high-purity nickel sulfate by an impurity-element removal method for selectively removing Mg from a Ni-containing solution. The method comprises a production process of producing nickel sulfate from a Ni-containing acid solution, the acid solution being treated in order of steps (1) to (3): (1) carbonation step, adding a carbonating agent into the Ni-containing solution to make Ni contained in the Ni-containing solution into a precipitate of nickel carbonate or a mixture of nickel carbonate and nickel hydroxide, thereby forming a slurry after carbonation including the precipitate and a solution after carbonation; (2) solid-liquid separation step, separating the slurry after carbonation formed in the carbonation step into the precipitate and the solution after carbonation; and (3) neutralization step, adding a neutralizing agent into the solution after carbonation separated through the solid-liquid separation step to recover Ni contained in the solution after carbonation as a Ni-precipitate.

Claims

1. A method comprising: providing a nickel-containing solution, treating the nickel-containing solution in order of the following steps of (1) to (3): (1) adding a carbonating agent to the nickel-containing solution, precipitating a carbonated nickel precipitate of nickel carbonate or a mixture of nickel carbonate and nickel hydroxide; (2) separating the carbonated nickel precipitate and a solution after carbonation; and (3) adding a neutralizing agent to the solution after carbonation, and therefrom recovering a nickel precipitate.

2. The method of claim 1, wherein the nickel-containing solution is a nickel sulfate solution.

3. The method of claim 2, wherein the nickel sulfate solution was obtained by leaching a nickel oxide ore with sulfuric acid, separating impurities other than a target component to obtain a residue, and adding a sulfurizing agent to the residue to form a nickel sulfide, and then leaching the nickel sulfide with sulfuric acid.

4. The method of claim 1, wherein the nickel-containing solution is a nickel sulfate solution obtained by leaching a nickel oxide ore with sulfuric acid, separating impurities other than a target component to obtain a residue, and adding a sulfurizing agent to the residue to form a nickel sulfide, and then leaching the nickel sulfide with sulfuric acid.

5. The method of claim 1 wherein the nickel-containing solution is a crude nickel sulfate solution; wherein the crude nickel sulfate solution includes nickel and magnesium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a production flowchart of high-purity nickel sulfate according to the present invention.

(2) FIG. 2 is a flowchart for a removal method of an impurity element from a nickel-containing acid solution.

(3) FIG. 3 is a chart showing relationships between an amount of sodium carbonate added and residual rates of Mg and Ca.

DETAILED DESCRIPTION

(4) The present invention provides a method for producing high-purity nickel sulfate from a nickel-containing acid solution, wherein a series of the undermentioned steps (1) to (3) is included in a production process in this order, whereby high-purity nickel sulfate having a less amount of impurities is produced from a nickel-containing acid solution.

(5) (1) A carbonation step, wherein a carbonating agent is added to a nickel-containing solution to make nickel contained in the nickel-containing solution into a precipitate of nickel carbonate or a precipitate of a mixture of nickel carbonate and nickel hydroxide, whereby a slurry after carbonation is formed, the slurry after carbonation being composed of a mixture of the precipitate and a solution after carbonation comprising an unprecipitated component other than the precipitate.

(6) (2) A solid-liquid separation step, wherein the slurry after carbonation formed in the carbonation step (1) is separated into the precipitate (nickel carbonate or the mixture of nickel carbonate and nickel hydroxide) and the solution after carbonation.

(7) (3) A neutralization step, wherein a neutralizing agent is added to the separated solution after carbonation through the solid-liquid separation step (2), whereby nickel contained in the solution after carbonation is separated and recovered as a nickel precipitate.

(8) Hereinafter, a method for producing a high-purity nickel sulfate solution according to the present invention will be explained with reference to a production flowchart for high-purity nickel sulfate shown in FIG. 1 and a flowchart of a method for removing an impurity element from a nickel-containing acid solution shown in FIG. 2 according to the present invention.

(9) Leaching Step

(10) The leaching step is a step of forming a leached solution (a nickel-containing acid solution) after leaching of nickel by dissolving, with mineral acid (hydrochloric acid, sulfuric acid, or the like), a nickel-containing material that serves as a starting material, such as an industrial intermediate, comprising any one selected from nickel-cobalt mixed sulfide, crude nickel sulfate, nickel oxide, nickel hydroxide, nickel carbonate, nickel powder, and the like, or a mixture thereof. This leaching step can be implemented using a well-known method, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2005-350766.

(11) Solution Purification (Neutralization) Step

(12) In the case of the use of an intermediate, such as sulfide produced from a solution obtained by leaching a nickel oxide ore, as the starting material, a large amount of valuables such as cobalt, and impurities not targeted for recovery are contained besides nickel to be targeted, and therefore these valuables and impurities need to be separated (Flow A in FIG. 1).

(13) Specifically, when the concentration of iron, chromium, or aluminum in the leached solution is high, the solution purification (neutralization) step is implemented to remove these elements before solvent extraction.

(14) Furthermore, using a solvent extraction method, cobalt, which is a valuable material and targeted for recovery, can be efficiently separated and recovered. However, magnesium, whose behavior resembles that of nickel, greatly affects the solvent extraction but can be easily separated by carbonation removal of impurities that is a removal method of impurity elements according to the present invention as mentioned later.

(15) Furthermore, a common production process of nickel sulfate uses an original solution containing high-concentration of nickel and low-concentration of impurity, but, it is more economical to apply the present invention to a solution containing magnesium, that is, impurity, in as high concentration as possible and nickel in as low concentration as possible because the amount of a carbonating agent used to precipitate nickel as a mixture of carbonate and hydroxide can be reduced. In that respect, in the solvent extraction step, a mixing ratio of an organic phase to an aqueous phase is optimized, whereby the concentration of an element in a solution can be easily adjusted, and therefore a desired solution can be easily achieved (Flow B in FIG. 1, a reaction in a direction indicated by a hollow arrow).

(16) Here, as a method for removing an impurity element according to the present invention, a carbonation removal method for impurities will be explained with reference to the flowchart in FIG. 2.

(17) Removal of Impurity Element from In-Process Solution

(18) (1) Carbonation Step

(19) In the carbonation step, a carbonating agent is added to an in-process nickel-containing material, particularly, an in-process nickel-containing solution (for example, a crude nickel sulfate solution) to precipitate nickel as nickel carbonate or a mixture of nickel carbonate and nickel hydroxide.

(20) At this time, since elements, such as cobalt, zinc, copper, manganese, and chromium, form carbonate or hydroxide in a lower range of pH than the pH range in which nickel forms carbonate or hydroxide, these elements are precipitated together with nickel and accordingly not separated. These elements are thus separated by a method such as the solvent extraction or neutralization precipitation.

(21) On the other hand, magnesium, sodium, potassium, and the like form carbonate or hydroxide less easily than nickel does, and these elements remain in the solution after carbonation, and therefore can be separated from nickel.

(22) The carbonating agent used at this time is not particularly limited, but, sodium carbonate has been industrially widely used, and is preferable because it is easily available in large amounts.

(23) The treatment temperature in the carbonation step is not particularly limited, but, preferably 40 to 80 degrees C.

(24) A treatment temperature of less than 40 degrees C. causes a too long reaction time, thereby leading to larger-scale equipment and higher investment costs. On the other hand, a treatment temperature of not less than 80 degrees C. prohibits a resin material from being used for equipment, thereby causing a material for equipment to be limited and costs to be increased.

(25) (2) Separation Step (Solid-Liquid Separation Step)

(26) The precipitate (nickel carbonate or the mixture of nickel carbonate and nickel hydroxide) contained in the slurry after carbonation formed in the carbonation step (1) and a solution after carbonation as a residue are separated and recovered using a solid-liquid separation apparatus.

(27) The solid-liquid separation apparatus to be used is not particularly limited, and a pressure filter, a suction filter, a decanter, or the like may be used. The mixture of nickel carbonate and nickel hydroxide which contains the recovered nickel as a main component can be reused by repeatedly using as a neutralizing agent in the solution purification step.

(28) (3) Neutralization Step

(29) The nickel carbonate or the mixture of nickel carbonate and nickel hydroxide, each having been separated as a precipitate in the solid-liquid separation step (2), can be reused as a neutralizing agent for pH regulation in another step.

(30) On the other hand, the solution after carbonation containing impurities after the solid-liquid separation forms a neutralized solution comprising a neutralized precipitate as a precipitate which is formed by the neutralization treatment implemented by addition of the neutralizing agent and contains heavy metals, such as manganese, and a solution after carbonation; and then the neutralization solution is solid-liquid separated using a solid-liquid separation apparatus, thereby being separated into the neutralized precipitate (nickel-containing precipitate) containing an impurity element and the solution after carbonation.

(31) The neutralizing agent to be used in the neutralization step is not particularly limited, but, sodium hydroxide, calcium hydroxide, magnesium hydroxide, or the like is inexpensive and thus suitably industrially used.

(32) For the neutralization, the pH is suitably adjusted to a range of from 7.0 to 8.5.

(33) This is because a pH of less than 7.0 leads to insufficient removal of manganese, on the other hand, a pH of more than 8.5 exceeds an effluent standard of pH value, and accordingly pH readjustment is required.

(34) Solvent Extraction Step

(35) Next, there is performed the solvent extraction step wherein an aqueous phase is made to come into contact with an organic phase thereby to exchange components of each of the phases to increase the concentration of a certain component in the aqueous phase, meanwhile to decrease the concentration of the other component therein. In the present invention, the solvent extraction step is implemented by a solvent extraction method wherein a crude nickel sulfate solution having a high concentration of impurity elements is used for the aqueous phase, meanwhile an organic solvent, such as phosphonic acid or phosphinic acid, or an nickel-containing organic solvent as disclosed in Patent Literature 2 is used for the organic phase, whereby a nickel sulfate solution and a stripped liquid are obtained.

(36) In this solvent extraction step, changing conditions for the solvent extraction enables to adjust the concentration of impurity elements in a nickel sulfate solution to be formed. In this regard, a nickel sulfate solution with concentrated impurity elements therein is formed by solvent extraction, and the impurity element removal method shown in FIG. 2 is given to the nickel sulfate solution again, whereby higher purity of a nickel sulfate solution can be formed.

(37) As mentioned above, the removal method of impurity elements from a nickel-containing acid solution is made to be included in the production process thereof, whereby magnesium can be selectively discharged from the production process system, and therefore these impurity elements are not accumulated inside the system, and as a result, high-purity nickel sulfate can be produced.

(38) Nickel sulfate produced according to the present invention is, as a product form, made into a nickel sulfate solution or made into a nickel sulfate crystal using a common crystallization method, such as crystallization or spray drying.

Example 1

(39) Hereinafter, using an example, the present invention will be further explained.

(40) A simulated solution of a crude nickel sulfate solution containing impurities was prepared as a nickel-containing material as shown in Table 1. Six 200-ml aliquots of the simulated solution were taken and each of the aliquots was put into a corresponding one of six beakers, and maintained at 40 degrees C. in a water bath. A sodium carbonate solution was dropped into the aliquots in such a way as that 0.08, 0.23, 0.45, 0.68, 0.91, and 1.18 equivalents of sodium carbonate with respect to nickel were added to each of the aliquots, and samples of No. 1 to No. 6 shown in Table 2 were thus produced.

(41) It should be noted that one equivalent mentioned here was calculated based on the following chemical reaction formula (1).
Formula 1
NiSO4+Na2CO3.fwdarw.NiCO3+Na2SO4(1)

(42) At the time of the dropping, stirring was kept for 30 minutes so as to stabilize the pH value and make the reaction sufficiently proceed. Then, using a vacuum pump, Nutsche suction filtration is performed with a 5C filter paper, so that a mixture of nickel carbonate and nickel hydroxide as a precipitate and a solution after carbonation as a filtrate are formed.

(43) Table 2 shows an amount of sodium carbonate added in the dropping, a nickel equivalent, a reaction temperature, a pH value, an amount of the filtrate, and an amount of the precipitate.

(44) Furthermore, each element contained in the solution after carbonations as a filtrate was quantitatively analyzed by ICP emission spectrometry. Table 3 and FIG. 3 show the results. In FIG. 3, the horizontal axis represents an equivalent amount of a chemical agent added with respect to nickel (nickel equivalent), and the chemical agent added was sodium carbonate. The vertical axis represents residual rates (%) of Mg, Ca, and Ni contained in the filtrate.

(45) TABLE-US-00001 TABLE 1 Ni [g/L] Co [g/L] Mg [g/L] Ca [g/L] Mn [g/L] 38 7.1 0.24 0.30 0.001

(46) TABLE-US-00002 TABLE 2 Addition Precipitate amount of Stirring Moisture Na.sub.2CO.sub.3 Temperature time pH Filtrate wet dry content No. [g] Ni equivalent [degrees C.] [min.] Initial Final [ml] [g] [g] [%] 1 1.2 0.08 40 30 4.69 6.38 202 5.77 1.26 78.2 2 3.4 0.23 4.73 6.33 200 18.82 6.09 67.6 3 6.8 0.45 4.80 6.37 208 35.35 11.59 67.2 4 10.2 0.68 4.81 6.45 223 48.49 12.88 73.4 5 13.7 0.91 4.85 6.74 215 65.64 20.06 69.4 6 17.7 1.18 4.89 7.54 231 64.29 22.57 64.9

(47) TABLE-US-00003 TABLE 3 Na.sub.2CO.sub.3 Filtrate + Ni Co Mg Ca Mn No. [g] Ni equivalent Free water [g/L] [g/L] [g/L] [g/L] [g/L] 1 1.2 0.08 207 36 6.7 0.24 0.30 0.001 2 3.4 0.23 232 28 5.5 0.21 0.24 <0.001 3 6.8 0.45 259 18 3.8 0.19 0.19 <0.001 4 10.2 0.68 261 10 2.2 0.17 0.13 <0.001 5 13.7 0.91 213 5.1 1.1 0.16 0.084 <0.001 6 17.7 1.18 273 0.31 0.064 0.097 0.015 <0.001

(48) As can be seen from Table 3 and FIG. 3, in the case where 1.2 equivalents of sodium carbonate with respect to nickel is added, not less than 99% of nickel is present in a precipitate, while 42% of magnesium is present in the precipitate and 58% of magnesium is present in a filtrate, and hence, it is understood that addition of a carbonating agent enables nickel and magnesium to be separated.