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Wet synthesis of high-density basic cobalt carbonate powder and thermodynamic analysis of Co(Ⅱ)-NH3-CO32--H2O system |
XU Wei1, XIA Jie1,2, ZHANG Kejun1, HU Bin1, BAI Dehong1, HE Kai1, YUAN Tiechui2, LI Ruidi2 |
1. Quzhou Huayou Cobalt New Material Co., Ltd., Quzhou 324000, China; 2. Powder Metallurgy Research Institute, Central South University, Changsha 410083, China |
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Abstract CoCl2 and four kinds of precipitants commonly used in industry, namely (NH4)2CO3, NH4HCO3, Na2CO3 and NaHCO3, were used as raw materials to prepare basic cobalt carbonate by wet synthesis. The as-prepared basic cobalt carbonate were studied by means of lazer particle analyzer, scanning electron microscope, X-ray diffractometer and vibrating densitometer. The effects of solution pH value and NH3 concentration on particle size, microscopic morphology, crystal structure and density of basic cobalt carbonate powder were evaluated, and the thermodynamic analysis of Co(II)-NH3-CO32--H2O system was performed as well. The results show that the pH value and NH3 concentration of the solution have a great influence on the complexation and precipitation behavior of cobalt ions. Based on the complexing precipitation process, the tap density of the basic cobalt carbonate solid powders prepared with NH4HCO3 and (NH4)2CO3 precipitant is higher. Based on the principle of simultaneous equilibrium and mass conservation, the thermodynamic diagram of lg[Co]total on pH under different solution compositions was drawn, and the effect of solution pH value of different systems on the precipitation process was further studied. The results show that the precipitation rate of cobalt ions is more than 90% when the pH is 6-8. In the Na2CO3 and NaHCO3 precipitant systems, free Co2+ is dominant during the transient, and it precipitates rapidly after contacting the precipitant to form loose flocculated basic cobalt carbonate powders. In the (NH4)2CO3 and NH4HCO3 precipitant systems, Co2+ is coordinated with ammonia, the precipitation process procees slowly with the release of Co2+ from multi coordinated Co(NH3)n2+ (n=1, 2,…, 6), results in dense powders.
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Received: 24 March 2022
Published: 19 July 2022
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