Process for the recovery of metals from oxidic ores

Abstract

A process is disclosed for the recovery of valuable metals from oxidic ores, in particular from polymetallic nodules. The process is suitable for the recovery of Cu, Co, Ni, Fe, and Mn, which are the main metals of interest in such polymetallic nodules. The present process is, among others, characterized by the handling of Fe, which is dissolved and kept in solution until the step of crystallization rather than removed at an earlier stage. A mixed MnFe residue is obtained, which, after thermal treatment, provides a MnFe oxide that is suitable for the steel or for the manganese industry. Excellent Cu, Co and Ni yields are obtained, while Fe is leached and valorized together with Mn.

Claims

1. A process for the recovery of Cu, Co, Ni, Fe and Mn from oxidic ores, comprising the steps of: dissolving the oxidic ores (P1) in acidic conditions using H.sub.2SO.sub.4 and SO.sub.2, thereby obtaining a Cu, Co, Ni, Fe, and Mn-bearing first solution (S1) and a first residue (R1); Solid/Liquid (S/L) separation of the first solution and of the first residue; recovering Cu (P2) by: precipitation as a sulfide by addition of a sulfide-bearing compound, or as a metal by addition of a metal more easily oxidized than Cu, thereby obtaining a Co, Ni, Fe, and Mn-bearing acidic second solution (S2) and a Cu-bearing second residue (R2) and S/L separation of the second solution and of the second residue; or by: extraction by electrowinning or solvent extraction (SX), thereby obtaining a Co, Ni, Fe, and Mn-bearing acidic second solution (S2) and a Cu-bearing stream; neutralizing (P3) the second solution (S2) to pH 2 to 5 by addition of first acid-consuming compounds, thereby obtaining a Co, Ni, Fe, and Mn-bearing neutralized third solution (S3); precipitating Co and Ni (P4) by adding a sulfide-bearing compound to the third solution, thereby obtaining an Fe and Mn-bearing fourth solution (S4) and a Co and Ni-bearing fourth residue (R4); S/L separation of the fourth solution and of the fourth residue; crystallizing Mn and Fe (P5) as sulfates from the fourth solution, thereby obtaining a fifth solution containing a minor part of the Mn (S5), and a fifth residue containing the major part of the Mn and of the Fe (R5); and S/L separation of the fifth solution and of the fifth residue.

2. The process according to claim 1, wherein, in the neutralization step, the first acid-consuming compound contains calcium, thereby obtaining a third residue (R3), and further comprising the additional step of S/L separation of the third solution and of the third residue.

3. The process according to claim 1, further comprising the steps of: splitting the fifth solution (S5) into a first fraction (S5a) and second fraction (S5b); recirculating the first fraction of the fifth solution to the step of dissolving (P1); precipitating Mn and Fe (P7) as carbonates or hydroxides by addition of second acid-consuming compounds to the second fraction of the fifth solution, thereby obtaining a sixth solution depleted in Mn and Fe (S6), and a sixth residue rich in Mn and Fe (R6); S/L separation of the sixth solution and of the sixth residue; and recirculating the sixth residue to the step of neutralization (P3), as at least part of the first acid-consuming compounds.

4. The process according to claim 1, comprising the steps of: thermal decomposition (P6) of the fifth residue, thereby obtaining an oxidic Mn-bearing seventh residue (R7) and SO.sub.2; separating the SO.sub.2; and recirculating the SO.sub.2 to the step of dissolving the ores (P1).

5. The process according to claim 1, comprising the steps of: reverse osmosis (P8) of the sixth solution, thereby obtaining water (S7) and concentrated salt solution (S8); and, recirculating the water to the step of dissolving the ores (P1).

6. The process according to claim 1, wherein the ores are deep sea nodules.

7. The process according to claim 1, wherein Cu is recovered from the first solution (S1).

Description

(1) FIG. 1 provides an overview of the flowsheet, also including the optional process steps and streams. The process steps are identified in Table 1, and the streams in Table 2.

(2) TABLE-US-00001 TABLE 1 Identification of the process steps according to FIG. 1 Process step ID Description P1 Dissolving the ores P2 Recovery of Cu P3 Neutralization P4 Precipitation of Co and Ni P5 Crystallization of Mn and Fe P6 Thermal decomposition P7 Precipitation of Mn (in bleed) P8 Reverse osmosis

(3) TABLE-US-00002 TABLE 2 Identification of product streams in FIG. 1 Stream ID Type Description R0 Feed Ores R1 Residue First residue, insoluble compounds in ores R2 Residue Second residue, when Cu is precipitated using H.sub.2S R3 Residue Third residue, when using CaCO.sub.3 as neutralizing agent R4 Residue Fourth residue, after Co and Ni are precipitated using H.sub.2S R5 Residue Fifth residue, after Mn and Fe are precipitated by crystallization R6 Residue Sixth residue, when Mn is precipitated from bleed stream R7 Residue Seventh residue, when the fifth residue is thermally decomposed S1 Solution First solution, leach solution bearing Cu, Co, Ni, Fe, and Mn S2 Solution Second solution, bearing Co, Ni, Fe, and Mn S3 Solution Third solution, neutralized, Co, Ni, Fe, and Mn-bearing S4 Solution Fourth solution, Mn and Fe-bearing S5 Solution Fifth solution, mother liquor containing a minor part of the Mn and Fe S5a Solution First fraction of fifth solution, recirculated to the step of dissolving S5b Solution Second fraction of fifth solution, bleed stream S6 Solution Sixth solution, depleted salt solution S7 Solution Seventh solution, essentially H.sub.2O S8 Solution Eighth solution, essentially a concentrated salt solution

(4) The disclosed process suitable for the recovery of Cu, Co, Ni, Fe, and Mn from oxidic ores, comprises the steps of dissolving the ores in acidic conditions, using H.sub.2SO.sub.4 and SO.sub.2, thereby obtaining a Cu, Co, Ni, Fe, and Mn-bearing first solution and a first residue, followed by S/L separation of the first solution and of the first residue.

(5) A suitable endpoint pH for this step would preferably be 2 or lower. Good leaching yields are then observed for the metals that are intended to be recovered, including Fe. The SO.sub.2 is directly injected in the leach solution in an amount that is preferably stoichiometric with respect to the metals to be reduced.

(6) According to a first alternative, the Cu in solution can be recovered by precipitation as a sulfide by addition of a sulfide-bearing compound, or as a metal by addition of a metal more easily oxidized than Cu, thereby obtaining a Co, Ni, Fe and Mn-bearing acidic second solution and a Cu-bearing second residue and S/L separation of the second solution and of the second residue.

(7) According to a second alternative, the Cu can be recovered by extraction, using electrowinning or SX, thereby obtaining a Co, Ni, Fe and Mn-bearing acidic second solution and a Cu-bearing stream.

(8) During this Cu recovery step, the pH may decrease somewhat due to the protons freed up, in particular when Cu is precipitated using H.sub.2S or NaHS as sulfide bearing compound. This decrease of pH has no detrimental effects other than requiring more acid-consuming compounds acting as neutralizing agents in the next process step, which is the neutralization to pH 2 to 5 of the second solution by addition of first acid-consuming compounds, thereby obtaining a Co, Ni, Fe, and Mn-bearing neutralized third solution.

(9) In a next step, Co and Ni are precipitated by addition of a sulfide-bearing compound to the third solution, thereby obtaining a Fe and Mn-bearing fourth solution, and a Co and Ni-bearing fourth residue, which are separated.

(10) During this Co and Ni recovery step, the pH may again decrease somewhat further due to the protons freed up. More neutralization agents may be added, to reach a pH of 2 to 7. It is indeed preferred to operate the next step, which is the crystallization of Mn and Fe, on a neutralized solution to avoid the corrosion of the equipment.

(11) In the neutralization step, CaCO.sub.3 may be used as acid-consuming compound. This produces gypsum, a solid that should preferably be separated in an additional S/L separation step. The production of solids requiring filtration can be avoided or minimized by using MnCO.sub.3 or Mn(OH).sub.2 as neutralization agent. These two products can advantageously be generated in the treatment of a bleed stream, as described below.

(12) Mn and Fe are recovered together from the fourth solution by crystallization, thereby obtaining a fifth solution (mother liquor) containing a minor part of the Mn, and a fifth residue containing the major part of the Mn and of the Fe. The crystals are separated from the mother liquor.

(13) Crystallization of Mn and Fe can be performed by evaporation. Alternatively, crystallization can be induced by heating, as the solubility limits of Mn and Fe decrease strongly with temperature. A temperature of more than 120 C., or even of more than 170 C. is then preferred.

(14) The mother liquor will still contain some residual dissolved Mn and Fe, as the crystallization will not fully exhaust these elements in the mother liquor. These metals can be recovered according to the following embodiment.

(15) Herein, the mother liquor is split in a first and second fraction, the first fraction being recirculated to the step of dissolving. The Mn and Fe in the second fraction (bleed stream) are precipitated as carbonates or hydroxides by addition of second acid-consuming compounds such as Na.sub.2CO.sub.3 or NaOH, thereby obtaining a sixth solution depleted in Mn and Fe, and a sixth residue rich in Mn and Fe, which are separated. Referring to the description above, it is advantageous to recirculate these carbonates or hydroxides as acid-consuming compounds to the step of neutralization.

(16) The bleed stream will also provide for an output to minor elements such as Na and K, which otherwise could accumulate to undesired levels when the process is run continuously. The second acid-consuming compounds are advantageously Na or K-based, as Ca-based compounds would lead to the dilution of the Mn in gypsum.

(17) Another embodiment concerns a process comprising the steps of thermal decomposition of the fifth residue, thereby obtaining an oxidic Mn-bearing seventh residue and SO.sub.2, and the separation and recirculation of the SO.sub.2 to the step of dissolving. The thermal decomposition in this process is achieved by heating the product to 850 to 1000 C.

(18) Another embodiment concerns a process comprising the steps of reverse osmosis of the sixth solution, thereby obtaining essentially pure water and a concentrated salt solution. The water can be reused in a previous step, e.g. for washing residues, and then recirculated to the step of dissolving the ores. The concentrated salt solution can be discharged.

(19) Another embodiment concerns any of the above processes, wherein the ores are deep sea nodules.

(20) The following examples further illustrate the invention.

EXAMPLE 1: NEUTRALIZATION USING CACO.SUB.3

(21) 1 kg (on dry) polymetallic nodules ground to D50 of 100 m is blended in 3.1 L water. The slurry is continuously stirred at 500 rpm and heated to 95 C. For 1.5 hours, a total of 510 g SO.sub.2 gas is blown into the slurry. Afterwards, 280 g H.sub.2SO.sub.4 is slowly added in 2 hours. During this addition, some SO.sub.2 is released from the solution resulting in 400 g being effectively consumed. A pH of 1.6 is reached. The slurry is separated by filtration. The solution contains 9 g/L H.sub.2SO.sub.4. The solids are washed.

(22) The Cu in the solution is precipitated in a first sulfide precipitation. The solution is thereby brought to 80 C. and continuously stirred at 300 rpm. Argon is blown over the liquid surface. For 2 hours, 6.2 g H.sub.2S (i.e. according to a 100% stoichiometry) is bubbled through the solution. The slurry is filtrated, and the solids washed with water and dried in a vacuum stove at 40 C. This solution now contains 14 g/L H.sub.2SO.sub.4.

(23) The solution needs to be neutralized to achieve a successful Ni and Co precipitation. To this end, the solution is brought to 75 C., stirred at 300 rpm, and argon is blown over the liquid surface. 51.2 g CaCO.sub.3 is brought in suspension in 0.15 L water. This slurry is slowly added to the solution. Gypsum is formed, which is separated. The pH of the solution then reaches the target value 3.

(24) Ni and Co are recovered from the solution using NaHS. The solution is brought to 70 C. and continuously stirred at 300 rpm. Argon is blown over the liquid surface. 264 mL NaHS solution containing 38 g S/L (i.e. according to a 120% stoichiometry) is added to the solution at a rate of 3 mL/min. The slurry is filtrated, and the solids are washed with water and dried in a vacuum stove at 40 C.

(25) The solution is loaded in an autoclave and brought to 176 C. Under these conditions, the solubility of both MnSO.sub.4 and FeSO.sub.4 decreases, resulting in their crystallization. The crystals are separated from the liquid phase using hot filtration to prevent redissolution of the crystals.

(26) The amounts and compositions of the different filtrates and residues are given in Table 3. The yields of the dissolving (P1) and precipitation steps (P2, P4, P5) are given in Table 4.

(27) TABLE-US-00003 TABLE 3 Amounts and compositions (solutions in L and g/L, residues in g and wt. %) Stream Mass Volume ID (g) (L) Mn Ni Co Cu Fe Si Al R0 1000.0 29 1.3 0.25 1.2 6.2 6.3 2.7 S1 3.59 80 3.6 0.69 3.2 12 0.0 2.2 R1 300.0 0.97 0.04 0.01 0.16 6.4 21 6.4 S2 3.59 80 3.6 0.69 0.0 12 0.0 2.2 R2 17.3 0.0 0.0 0.0 66 0.0 0.0 0.0 S3 3.74 77 3.4 0.66 0.0 11 0.0 2.1 S4 3.74 77 0.0 0.0 0.0 11 0.0 1.8 R4 28.1 1.0 46 8.8 0.0 1.5 0.0 3.9 S5 3.66 9 0.0 0.0 0.0 1.7 0.0 0.06 R5 900.45 28 0.0 0.0 0.0 4.0 0.0 0.7

(28) TABLE-US-00004 TABLE 4 Metal yields (in %) per process step Process step ID Mn Ni Co Cu Fe Si Al P1 99 99 99 96 69 0 29 P2 0 0 0 100 0 0 0 P4 0.1 100 100 100 1 0 14 P5 88 0 0 0 85 0 97

(29) The metal yields per process step are considered as most satisfying.

EXAMPLE 2: NEUTRALIZATION USING MNCO.SUB.3

(30) This Example is analogous to Example 1. However, recirculated Mn and Fe carbonates are used as neutralizing agent instead of CaCO.sub.3. Consequently, no gypsum is formed, and the corresponding filtration step is eliminated.

(31) After the Cu precipitation, the solution needs to be neutralized. To this end, a fraction of the pumpable slurry, prepared as shown below, is slowly added to the solution as acid-consuming compounds. When adding an amount containing 58.8 g of a mixture of Mn and Fe carbonates, the pH of the solution reaches the target value of 3.

(32) Mn and Fe are then recovered by crystallization, according to Example 1.

(33) The Mn and Fe still present in the mother liquor after the crystallization step are precipitated as carbonates by the addition of 66.8 g Na.sub.2CO.sub.3. The slurry is filtrated, and the residue is washed and dried. It contains 92.4 g of a mixture of Mn and Fe carbonates. This residue is then diluted with 0.28 L water to create a pumpable slurry. Part of this slurry is used as acid consuming compounds in the above-described step.

(34) It should be noted that in a continuous process, it would be advantageous to perform the precipitation step on only a fraction of the mother liquor, this fraction being determined by the need for acid-consuming compounds in the neutralization step. The remainder of the mother liquor can then be recirculated to the dissolution step.

(35) The amounts and compositions of the different filtrates and residues are given in Table 5. The yields of the dissolving (P1) and precipitation steps (P2, P4, P5) are given in Table 6.

(36) TABLE-US-00005 TABLE 5 Amounts and compositions (solutions in L and g/L, residues in g and wt. %) Mass Volume Stream ID (g) (L) Mn Ni Co Cu Fe Si Al R0 1000.0 29 1.3 0.25 1.2 6.2 6.3 2.7 S1 3.59 80 3.6 0.69 3.2 12 0.0 2.2 R1 300.0 0.97 0.04 0.01 0.16 6.4 21 6.4 S2 3.59 80 3.6 0.69 0.0 12 0.0 2.2 R2 17.3 0.0 0.0 0.0 66 0.0 0.0 0.0 S3 3.77 83 3.4 0.66 0.0 13 0.0 2.1 S4 3.77 82 0.0 0.0 0.0 12 0.0 1.8 R4 28.2 1.1 46 8.8 0.0 1.7 0.0 3.9 S5 3.67 10 0.0 0.0 0.0 1.9 0.0 0.06 R5 973.2 28 0.0 0.0 0.0 4.1 0.0 0.7 R6 58.8 40 0.0 0.0 0.0 7.6 0.0 0.0

(37) TABLE-US-00006 TABLE 6 Metal yields (in %) per process step Process step ID Mn Ni Co Cu Fe Si Al P1 99 99 99 96 69 0 29 P2 0 0 0 100 0 0 0 P4 0.1 100 100 100 1 0 14 P5 88 0 0 0 85 0 97

(38) Even though the yields per process step are equally satisfying as in Example 1, the overall Mn yield will be higher when applying the neutralization method according to Example 2. Indeed, most of the Mn in the mother liquor after crystallization will in this case be recovered and brought out in the crystallization step.