Studies on Leaching and Recycling of Zinc from Rayon Waste Sludge

Abstract

Zinc is an important nonferrous metal used in various metallurgical, chemical, and textile industries. In textile industries, a waste sludge containing zinc hydroxide is generated during the manufacture of rayon yarn. The two sludge samples were used for the experimental work. The National rayon contained a high value of zinc (18.90%), 13.0% Ca, and 7.63% Si, whereas the sample from Baroda rayon contained a low value of zinc (5.12%), 19.2% Ca, and 5.60% Si. The impurities present in both of the samples are iron, aluminum, magnesium, silica, etc. The leaching studies were carried out using alkaline, ammoniacal, and acidic solutions at different concentrations of the lixiviants at room temperature. Sulfuric acid has been found to be the suitable reagent for complete dissolution of zinc. On the basis of the results of kinetic studies of the leaching in sulfuric acid medium, a chemical reaction control dense constant size cylindrical model has been proposed as the experimental data that fit most satisfactorily with the equation 1 − (1 − X) 1/2 = K c t for both the sludge samples. The solution could be purified for subsequent metal recovery. The residue produced after zinc recovery could be disposed of safely without affecting the environment.