Disposal of highly toxic waste chromium solutions

Abstract

The aim of the study is to determine the effect of organic reductants (sawdust) on the degree of reduction of chromium (VI) ions in the complex processing of waste chromium-containing solution (electrolyte) of plating production, as at the same time to determine the optimum conditions of the process. Experimental results showed that organic reductants (sawdust, and lignin) in an acid environment work as a reagent-reductant of chromium (VI) ions. The process of reduction of chromium (VI) ions to chromium (III) proceeds intensively for the first 20-30 min and is completed within 50 minutes, while about 1.0-2.5% of chromium (VI) ions remain unreduced, and 97.0-99.0% of chromium (VI) ions of the total amount pass into trivalent form. Chromium (VI) ions are reduced at the first stage of the process, the bulk of them are converted into chromium (III) ions and emitted as chromium (III) hydroxide, and wastewater is further purified at the second stage. When using lignin, the reduction in the concentration of chromium (VI) ions is insignificant, since the number of active functional groups in its structure is limited. Model studies presented in this work and their approbation on production wastewater showed expediency and sufficiently high efficiency of using woodworking wastes (sawdust) to reduce chromium (VI) ions from the spent solutions. Sawdust consists mainly of cellulose; its structure contains functional groups that act as a reductant during oxidation. Further study of the process mechanism and characteristics is essential for the development of recommendations for their utilization.