Fine nickel(Ni) powders with controllable particle sizes were synthesized via the reduction of nickel hydrazine complex precursors of pure [Ni(N2H4)2]Cl2 and a mixture of [Ni(N2H4)2]Cl2 and [Ni(N2H4)3]Cl2 in aqueous solution. The mechanism of the formation of metallic Ni powders experiences the reduction of nickel hydroxide by hydrazine released from the ligand exchange reaction between nickel hydrazine complex and NaOH. In comparison with the method of preparing Ni powders from nickel salts,the method of making Ni powders via the reduction of nickel hydrazine complex precursors shows the advantages of using half dosage of hydrazine for complete reduction of nickel ions in solution,and the obtained Ni particles show less agglomeration and better dispersibility. Moreover,the average particle size of nickel powders can be controlled from 180 to 260 nm by adjusting the reaction molar ratio and concentration.
Three kinds of dialkylphosphinic acids(DAPAs),i.e.dihexylphophinic acid(DHPA),di-(2,4,4-trimethylpentyl) phosphinic acid(DTMPPA)and didecylphophinic acid(DDPA),were synthesized through free radical addition reaction.The influence of the types of initiator,reation time and reaction temperature on the yield of DAPAs were investigated.The products were characterized by NMR and MS.By using DHPA,DTMPPA and DDPA(10%in kerosene)as extractants,the extraction of Co2 +and Ni2 +in sulphate medium at different equilibrium pH values were measured.The results show that the maximum yield of DHPA, DTMPPA and DDPA can all be achieved at about 130℃under the initiation of di-tert-butyl peroxide(DTBP).All the extraction of cobalt with respect to DHPA,DDPA and DTMPPA precedes that of nickel.The difference in pH1/2 value(defined as the pH at which 50%metal extraction occurs)between cobalt and nickel increases in the following sequence from large to small:DHPA,DDPA and DTMPPA,which indicates that the separation ability for cobalt and nickel ascends from DHPA,DDPA to DTMPPA.
