Flotation separation of maghara coal in Egypt for the removal of hazardous Cr(VI) from industrial wastewater

Abstract

ABSTRACT Due to its serious toxicity, wastewater contaminated with hexavalent chromium (Cr(VI)) has become an increasing environmental concern. Herein, a novel flotation separation of maghara coal in Egypt for Cr(VI) removal was proposed to separate coal to three types of maceral group fractions including liptinite, vitrinite, and inertinite via controlling in density as a function in the degree of coalification. The results implied that the activated inertinite macerals (AIM) have the highest carbon and lowest nitrogen levels among the entire maceral groups. The Langmuir isotherm model exhibited a high adsorption capacity of the AIM sample (1226. 21 mg/g) compared to pre-flotation separation sample (877.55 mg/g). Therefore, the flotation separation of maghara coal played a vital role in the Cr(VI) removal. The residuary concentration of Cr(VI) after adsorption onto AIM was close to 0.037 mg L−1 at pH = 2, which satisfies the industrial wastewater discharge standard. In addition, the removal of Cr(VI) onto AIM surface has been demonstrated to be highly effective via the adsorption and reduction process. The oxygen-containing functional groups could strengthen the interaction between Cr(VI) and AIM surface through the reducing reactions. The accelerating effect of organic acids was investigated for the capture of Cr(VI) and the efficiency in the presence of tartaric acid was improved up to 99.96% within 48 h compared to other organic acids. Therefore, this research provides a sophisticated strategy for separating coal to highly efficient adsorbents for wastewater remediation.