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The process and production practice of nickel and cobalt from activated magnesium oxide in DRC: raw and auxiliary materials and production process

Congo (Kinshasa) is the country with the largest reserves of cobalt resources in the world, and its production capacity accounts for more than half of the world\’s total production. Cobalt resources in Congo (DRC) mainly exist in the form of copper-cobalt symbiotic ores, and a few are independent cobalt ores. The hydrometallurgy of copper-cobalt ore generally adopts the leaching-extraction-electrodeposition process to produce cathode copper, and the cobalt-containing raffinate after copper extraction generally adopts the impurity removal-cobalt precipitation process to produce cobalt salts or cobalt compounds. The impurity removal process generally uses the neutralization and hydrolysis method to remove impurities such as iron ions and iron ions in the solution. The neutralizer generally uses lime or slaked lime, and the oxidation removal (iron, manganese, etc.) method usually includes sulfur dioxide Mixed gas oxidation with air, strong oxidant (sodium chlorate etc.) Contaminant sodium ions are introduced into the system. The sulfur dioxide and air mixed gas oxidation method has the advantages of relatively low potential to avoid cobalt loss and not introduce impurity ions.

The cobalt precipitation process generally uses a precipitant to separate cobalt ions from the solution by forming insoluble cobalt salts or cobalt compounds. Precipitating agents used in the cobalt precipitation process usually include HS, sodium salt, etc. HS is toxic, harmful to human health and easy to cause environmental pollution. Sodium salts such as Na, CO, NaOH, etc. have strong alkalinity, and it is easy to form a solution that partially enters an environment with an excessively high pH, ​​causing other impurity ions in the solution to precipitate together with cobalt ions, resulting in lower cobalt grades in cobalt products and higher impurities. Moreover, the use of sodium salts will introduce sodium ions into the system and be difficult to handle. When the concentration of sodium ions is high, production will be adversely affected. Activated magnesia has weak alkalinity and is relatively safe to use, and the wastewater after cobalt precipitation is easier to treat.

This paper provides a new process of removing impurities from cobalt-containing raffinate, cobalt precipitation in the first stage, cobalt precipitation in the second stage of slaked lime, and magnesium precipitation in slaked lime to produce high-grade cobalt hydroxide. The influence of cobalt, and organized trial production according to the whole process. The trial production results show that the selected process is suitable for the production of high-grade cobalt hydroxide. The cobalt grade in the cobalt hydroxide product obtained in the first stage of cobalt precipitation reaches 32%, the cobalt recovery rate of the whole process reaches more than 96%, and the magnesium precipitation wastewater can be returned as production use water.

1. Raw materials and accessories

1.1 Raw material

The cobalt sulfate solution used for production is the cobalt-containing stalk residue after stirring leaching and extraction of a copper-cobalt mine in the Democratic Republic of the Congo. Its typical chemical composition is shown in Table 1.

1.2 Add the main auxiliary materials

Slaked lime: for industrial use, -200 mesh>90%, CaO>70%;

Magnesium oxide: for industrial use, -325 mesh>99%, MgO>90%;

Sulfur dioxide: acid flue gas (SO₂ concentration 7.5%).

2. Processing flow

The treatment process is mainly composed of impurity removal, first-stage cobalt precipitation, second-stage cobalt precipitation, magnesium precipitation and cobalt hydroxide drying. Impurity removal is to add slaked lime to the cobalt-containing raffinate, and pass a certain proportion of sulfur dioxide and air mixture gas, so that the low-valent iron and manganese ions in the solution are oxidized into high-valent iron and manganese ions, which are hydrolyzed at a certain pH to form Precipitation and separation of valuable cobalt ions. The first stage of cobalt precipitation is to add magnesium oxide to the liquid after impurity removal, so that the cobalt ions in the solution enter into the precipitation to obtain the cobalt hydroxide product. The second-stage cobalt precipitation is to add slaked lime to the first-stage cobalt precipitation liquid to recover the incompletely precipitated cobalt ions, and the second-stage cobalt slag returns to the iron removal and redissolves into the impurity removal liquid. Magnesium precipitation is to add slaked lime to the solution after cobalt precipitation in the second stage to remove impurities such as magnesium ions in the solution, realize the reuse of magnesium precipitation wastewater, and store magnesium slag separately.

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