INVESTIGATION OF REACTION STOICHIOMETRY OF LEACHING OF SYNTHETIC CaWO_4 IN H_2C_2O_4 SOLUTIONS

摘要

In this study, leaching characteristics of CaWO_4 in H_2C_2O_4 solutions and reaction stoichiometry were investigated. Solutions were taken from the reactor and dissolved Ca and W were analyzed quantitatively by ICP-OES instrument. Leach residues and solid products obtained by evaporation of leach solutions were characterized by XRD, TGA-DTA-MS and FT-1R analyses. It was found that leaching reaction took place via decomposition of Ca[WO_3(C_2O_4)H_2O] intermediate chelate compound formed in the first step to H_2[WO_3(C_2O_4)H_2O] final chelate compound formed in the second step. It was also seen that H_2[WO_3(C_2O_4)H_2O] chelate compound was not stable and it began to decompose by forming H_2WO_4 precipitate after a certain time. Overall leach reaction was determined as CaWO_(4(s)) + 2 H_2C_2O_(4(aq)))+ H_2O_((1)) - H_2[WO_3(C_2O_4)H_2O]_((aq))+ CaC_2O_4H_2O_((s)).