Kinetic investigation of dissolution of CaWO4 in oxalic acid solution

Abstract

In this study, the effects of stirring speed, temperature, H2C2O4 concentration and particle size on the dissolution rate of CaWO4 in H2C2O4 solutions were investigated. CaWO4 was dissolved in H2C2O4 solutions as series parallel type reaction. In the first step which took place according to Langmuir-Hinshelwood Mechanism, H2C2O4 was adsorbed as a mobile adsorption layer on the surface of CaWO4, reacted to form adsorbed calcium aqua oxalato tungstate (Ca[WO3(C2O4)H2O]) intermediate product and the adsorbed Ca[WO3(C2O4)H2O] was desorbed into the solution. In the second step, Ca[WO3(C2O4)H2O] hydrolysed and formed H2WO4 which reacted with H2C2O4 to form hydrogen aqua oxalato tungstate (H-2[WO3(C2O4)H2O]) as end product together with solid CaC2O4H2O. Model kinetic equations were derived which showed the relationships of the fractional conversion of CaWO4, the concentration of Ca[WO3(C2O4)H2O] and the concentration of H-2[WO3(C2O4)H2O] with time. The diagrams drawn according to the model kinetic equations were in good agreement with the experimentally obtained diagrams (R-2>0.99).