Magnesium recycling and sulphur recovery in leaching of lateritic nickel ores
The present invention resides in a process of recovering nickel and cobalt, regenerating the main raw materials, said process including the steps of: granulometric separation; leaching; neutralization; MHP production in only one stage and the pressure crystallization of magnesium sulphite. The process proposes a way to recovery nickel and cobalt from laterite ores through the atmospheric and heap leaching with staged addition of ore—by size separation—and H 2 SO 4 , decreasing the nickel losses and simplifying the neutralization circuit and producing a more purified MHP. The present process route is employed for nickel extraction, including the one from high magnesium containing lateritic ores.
1. A magnesium recycling and sulfur recovery method in leaching of lateritic nickel ores, the method comprising the steps of:
(I) granulometric separation of coarse and fine material;
(II) heap leaching of the coarse material and atmospheric leaching of the fine material;
(III) neutralization of the leached material with addition of a first concentration of MgO pulp in two stages to increase the pH value up to approximately 2.5 during a first stage, and then up to approximately 4.5 during a second stage via addition of a second concentration of MgO lower than the first concentration, and to hydrolyze the iron, aluminum and copper;
(IV) solid-liquid separation of the neutralized leached material;
(V) purification of the separated solid with a diluted solution of H 2 SO 4 in combination with a reducing agent;
(VI) manganese removal from the purified separated solid using ozone gas in conjunction with MgO; and
(VII) crystallization under pressure to promote recovery of MgSO 4 .
2. The method according to claim 1 , wherein the granulometric separation comprises guiding coarse material with a grain size greater that 0.5 mm to heap leaching, and fine materials with a grain size lower than 0.5 mm to atmospheric leaching in agitated tanks.
3. The method according to claim 1 , wherein a leaching solution for heap leaching is prepared with regenerated sulphuric acid along with water generated during pressure crystallization and containing sulphuric acid concentration between 50 to 300 g/L.
4. The method according to claim 1 , wherein at the atmospheric leaching stage, there is low sulphuric acid consumption according with the granulometric size and the reducing agent comprises SO 2 .
5. The method according to claim 1 , wherein the reducing agent is at least one of metallic iron, metallic nickel, magnesium sulphite, sodium sulphite, sodium hydrosulphite, sodium bisulphate, or magnesium bisulphate.
6. The method according to claim 2 , wherein in the first stage of the atmospheric leaching, an ore with a maximum grain size between approximately 0.5 mm and approximately 0.077 mm is used together adding up effluent from the heap leaching and at temperatures between 70 to 100° C. and a total-time of 1 to 4 hours.
7. The method according to claim 2 , wherein in the second stage of the atmospheric leaching, an ore with a maximum grain size between 0.154 mm to 0077 mm is added to the material from first stage at temperatures between 70 to 100 Celsius degree and total residence time of 4 to 8 hours.
8. The method according to claim 1 , wherein the addition of the MgO pulp is made in a higher concentration in the first stage in the range of 10 to 30% by weight, and in a lower concentration in the second stage in the range of 1 to 5% MgO by weight.
9. The method according to claim 8 , wherein the two stages of the neutralization occur between 70 to 100° C.
10. The method according to claim 1 , wherein the pH value in the neutralization step is between 1.5 to 2.5 during the first stage and between 4.0 to 4.5 during the second stage.
11. The method according to claim 1 , further comprising adding MgO subsequent to solid-liquid separation to raise the pH value between 7.2 and 9.0.
12. The method according to claim 11 , wherein the solid liquid separation occurs at temperatures between 40 to 80° C.
13. The method according to claim 1 , wherein in the purification stage the H 2 SO 4 solution is utilized in the range of 1 to 5%, the pH is between 7 to 8 and the reducing agent reduces Mn +4 to Mn +2 and sulphuric acid redissolve the MgO co-precipitated.
14. The method according to claim 1 , wherein the crystallization is carried at a temperature in the range of 190 to 240° C.
15. The method according to claim 1 , wherein crystals obtained at the crystallization step are sent to a furnace and react with a reducing agent generating MgO and SO 2 gas.
16. The method according to claim 14 , wherein the recovery of MgSO 4 is done using crystallization by evaporation or by common ion effect.
17. The method according to claim 6 , wherein the temperatures are between 95 and 100° C.
18. The method according to claim 8 , wherein the addition of the MgO pulp in the first stage is 20% MgO by weight, and in the second stage is 2% MgO by weight.
19. The method according to claim 9 , wherein the two stages of the neutralization occur between 95 and 100° C.
20. The method according to claim 12 , wherein the solid liquid separation occurs at a temperature of 60° C.
21. The method according to claim 13 , wherein the pH is 7.5.
22. The method according to claim 14 , wherein the crystallization is carried at a temperature of 220° C.