Precipitated green pigments: products of chromate postgalvanic waste utilization.

The paper reports on obtaining highly dispersed chromium(III) silicates and chromium(III) oxides from postchromating waste by reduction of Cr(VI) to Cr(III) with hydrazine as a reducing agent. Chromium(III) salt solution and sodium silicate or hydroxide solutions have been used to precipitate green pigments (silicates and oxides). The effect of the precipitation parameters on the quality of green pigments obtained has been studied, and the optimum parameters ensuring getting the product of well-developed surface area and possibly lowest diameter of primary particles have been established. The precipitated silicates and oxides have been subjected to physicochemical analysis to determine bulk density; capacities to absorb water, dibutyl phthalate, and paraffin oil; particles size; particle size distribution; and surface morphology of chromium pigment surfaces. The adsorptive properties of the oxide and silicate pigments have also been examined. The XRD analysis documented that the chromium(III) silicate pigments obtained are amorphous. In addition, the pigments have been subjected to a colorimetric appraisal using the CIE L*a*b* color space system. The high-quality green pigments obtained have shown high dispersion, small tendency to agglomerate formation, and repeatable green hue. The parameters of the products are promising for their future technological use.