Study On The Mechanism Of Nickel Chloride Chlorination

Dwindling nickel sulphide ore makes the development and utilization of laterite nickel ore being paid more and more attention by the majority of researchers.Chloride segregation of laterite nickel ore is an exceptional and promising technics for its less process,low energy consumption,and strong adaptability to the ore.However,the mineral composition of the laterite is varied and complex,which leads to the reaction during chloride segregation is multitudinous and complicated,so the research treating laterite as a reactant directly is inconvenient to convey the mechnism understandably.Therefore,this paper treated representative pure Ni O and NiCl₂ as reactants on the basis of decomposing chloride segregation of laterite nickel as two parts: chlorination of valuble metal oxides by chloride salt and reduction of the valuble chloride newly generated.The main research contents are as follows:?i?The chlorination stage focused on decompsition of MgCl₂·6H₂O and CaCl₂·6H₂O as well as the reaction of these chloride chloridizing NiO.The effects of SiO₂,Fe₂O₃,CaO?MgO?on the yield of HCl?g?generated by MgCl₂·6H₂O and CaCl₂·6H₂O and the favorable chlorination condition were investigated,and the relationship between the HCl?g?yield and chlorination efficiency was analysed in brief.The results showed that,the yield of HCl?g?obtained by heating CaCl₂·6H₂O?up to 34.5%?was much lower than that of MgCl₂·6H₂O?up to 87.95%?.Both SiO₂ and Fe₂O₃ promoted MgCl₂·6H₂O and CaCl₂·6H₂O to generate HCl?g?at higher temperature as a result of these two additive agents reacted with MgCl₂·6H₂O as well as CaCl₂·6H₂O or their analytes,these additives could lower the temperature of MgCl₂·6H₂O decomposing completely from 900? to 800? and increase the HCl?g?yield of CaCl₂·6H₂O at 1000 ? to 51.94% and 42.93% respectively.CaO reduced the HCl?g?yield of MgCl₂·6H₂O to a level lower than 35%.The combined action of CaO and SiO₂ on the HCl?g?yield of MgCl₂·6H₂O was less negative than the effect of only CaO;MgO and SiO₂ acted on CaCl₂·6H₂O would raise HCl?g?yield significantly.The chlorination efficiency of NiO using either MgCl₂·6H₂O or CaCl₂·6H₂O as chlorinating agents was a function of temperature,which increased at first and decreased later on as roasting temperature going up.The best result was obtained when temperature was 600?,and the chlorination efficiency were 14.44%?MgCl₂·6H₂O as the agent?and 0.18%?CaCl₂·6H₂O as the agent?at a mole ratio?chlorinating agents : NiO?of 1:1.More chlorination agents brought higher chlorination rate.SiO₂ promoted the chlorination reaction as it boosted these two salt to decompose,but its existence reduced the chance of HCl?g?contacting NiO meanwhile,for which an oversized addition led to a lower efficiency.In general,Fe₂O₃ did not promote chlorination of NiO,and it lower the efficiency obviously in the range of 400⁷00?.?ii?In reduction part,better reducing temperature,the best addition of reducing agent and the impact of SiO₂ and Fe₂O₃ was mainly examined.The results showed that,both raising temperature and increasing the addition of charcoal powder promoted the reduction.At the addition of 0.24 g charcoal powder per 0.01 mol NiCl₂,the reduction rate rose to 32.56% from 6.64% when roasting temperature rose from 600? to 900?.Some NiCl₂ escaped out of the crucible at 1000?,so the calculated reduction rate was lower.The reduction rate would stay at a level when the dosage of reducing agent was over 0.24 g per 0.01 mol NiCl₂.SiO₂?as well as a mixture of SiO₂ and CaO?promote the reduction of NiCl₂ to Ni,the reduction rate at 900? came up to 37.18% from 32.56% after adding SiO₂ to the mixture of 0.24 g reducing agent and 0.01 mol NiCl₂.The addition of Fe₂O₃ went against the reduction of NiCl₂ because Fe₂O₃ was more easily to be reduced than NiCl₂.?iii?FactSage software was used to draw NiO-HCl-C predominance area diagram and NiCl₂-C-H₂ O predominance area diagram to analyse the whole chlorination segregation process of NiO.With regard to NiO-HCl-C system at atmospheric pressure,higher temperature made chlorination reaction more difficult and main elemental Ni was obtained by the direct reduction of NiO rather than NiCl₂,which was probably caused by the deficiency of H₂O?g?.From NiCl₂-C-H₂ O predominance area diagram,it could be concluded that Ni element was obtained by reduction of NiCl₂ rather than its hydrolysis product NiO.Raising temperature would promote the hydrolysis of NiCl₂,and the product NiO was more difficult to reduce than NiCl₂.Increasing the addition of C may be effective to inhibit the hydrolysis of NiCl₂.