Study of Behavioral about the Decomposition Reaction of the Solid Solution KFe3(SO4)2-x(CrO4)x(OH)6 in Ca(OH)2 Media

The decomposition of the solid solution KFe₃(SO₄)_2-x(CrO₄)_x(OH)₆ and its capacity to detain CrO₄2- under alkaline conditions were studied. A solution of Ca(OH)₂ was the media used. The incorporation of CrO₄2- in crystalline structure of jarosite, resulted in a solid solution with the following approximate formula: [K_0.86(H₃O)_0.14]Fe_2.67[(SO₄)_1.23(CrO₄)_0.77][(OH)_5.01(H₂O)_0.99]. The experimental data describe a reaction based in the model of decreasing core with chemical control. Decomposition curve shows an induction period, characterized by the formation of active centers where is initiated and established a reaction front, that is the beginning of the progressive conversion period, during which is formed a layer of inert products of Fe(OH)₃ and is characterized for the massive diffusion of K+, SO₄2- and CrO₄2- toward the solution. However, the mappings by SEM-EDS from a particle decomposed partially, shows that the SO₄2- is released preferentially, meanwhile, an important quantity of the CrO₄2- is adsorbed in the layer of Fe(OH)₃.