Study On Novel Technology And Basic Theory Of Removing Copper From Nickel Sulfide Anodic Electrolyte

Separation of copper from nickel solution has been difficult due to their similar chemical propertities, and thus it was included in the national important projects of the Eighth and Ninth "Five Year plan". And removing copper with "active nickel sulfide" was performed in commercial experiments. In 2004, it was taken as a technic nut to invite bids all over China by Jinchuan Group Ltd. Owing to its great difficulty, the related technical standards have to be covered. For example, the concentration of copper is decreased from 3mg·l^-1 (4.72×10^-5mol·l^-1) to 2mg·l^-1 (3.15×10^-5mol·l^-1) and the mass ratios of copper to nickel from 20 to 15.It seems that removing copper by sulfidation is a sound methold since copper has strong affinity for sulfur. NiS, which was used as a kind of reagent for removing copper in the technology of "active nickel sulfide", is regarded as leading compounds. New highly effective copper-removing reagents are obtained through lead generation by molecule modification based on the theory of isostere principle. On the one hand, MnS copper-removing reagent is obtained by replacing nickel with manganese through modifying cation. On the other hand, another new copper-removing reagent NAS is obtained by replacing S^2- with a kind of new chemical structure through modifying anion.The present study mainly includes the following.The equilibrium in the systems of Cu-Ni-Cl-S-H₂O and Cu-Ni-Mn-Cl-S-H₂O is analysised through thermodynamic calculation. The results show that cupric mainly exists in the form of chlorine—complexes. When there are S^2- ions in the system, nickel exists in the form of free nickel ions, while the concentration of Ni(HS)⁺ and Ni(HS)_2(aq) is much lower than that of nickel ions. Copper exists in the form of Cu(HS)⁺ and especially in the form of Cu(HS)_2(aq). The concentration of [Cu(HS)_2(aq)] affects copper-removing effect. The thermodynamics analysis in the system of Cu-Ni-Mn-Cl-S-H₂O shows that MnS can act as a kind of copper-removing reagent and can satisfy to the removal of copper.The experiment of removing copper with manganese sulfide shows that MnS still keeps active after the aging time of 102 hours, and the concentration of copper in the treated aqueous solution is less than 1.57×10^-5mol·l^-1, and the mass ratio of copper to nickel is up to 20 under the following conditions. The dosage of manganese sulfide is 1.2 times of theoretical value, the reaction temperature is higher than 50℃, the solution pH value is between 4.0 and 6.0, and the reaction time is 90 minutes. Moreover, the ions of manganese in the treated aqueous solution can be effectively removed by adding oxidant.Removing copper with NAS will achieve the best result when reaction rate of A-S,α, is more than 73%, the dosage of NAS is 1.2 times of theoretical value, and when pH value is between 4 and 5 at the temperature of higher than 50℃. The concentration of copper can reach 1.57×10^-6mol·l^-1 in the electrolyte solution and the mass ratio of copper to nickel is more than 25 in the residue after removing copper. Especially, after NAS has been kept for 62 days or 1500 hours, it can still satisfy the demand of removing copper if NAS is used to remove copper. Moreover, we have studied the technology of preparation of NAS with A-S and its characterization. Results show that copper sulfide, with small solubility product constant, is produced after removing copper with NAS.The kinetic process of the reaction of sodium sulfide and A-S is investigated. The activation energy and reaction progressions of the process are 7.2 kJ·mol^-1and 0, respectively. The kinetic process of the reaction of removing copper with NAS is also studied. The results show the reaction is so quick that its reaction rate can reach or exceed 80% during the first 10 seconds, which provides some foundations for the further study.The technology and economy analysis of the three methods of removing copper with nickel ore, manganese sulfide and NAS is comprehensively made. Their relative cost can be calculated in a simple way. Compared to the present technology of removing copper in Jinchuan Group Ltd., the cost of removing copper with manganese sulfide is less 893.89 yuan per ton, and the cost with NAS is less1446.36 yuan per ton.