JI Xiang, DING Hong-rui, LI Yan-zhang, LU An-huai*, WANG Chang-qiu, LI Yan

(Key Laboratory of Orogenic Belts and Crustal Evolution of Ministry of Education and Beijing Key Labroratory of Mineral Environmental Function, School of Earth and Space Sciences, Peking University, Beijing 100871, China)

Abstract: In this paper, natural magnetite was used to assist artificially synthesized pyrrhotite for removing hexavalent chromium from aqueous solution. Experimental results had verified that there is synergistic enhancement effect between magnetite and artificially synthesized pyrrhotite in the process of the removal of hexavalent chromium. By using X ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and the X-ray energy dispersive spectroscopy (EDS), the original samples and reacted samples were analyzed. We have found that the hexavalent chromium in the aqueous solution is effectively reduced into the trivalent chromium, by the artificially synthesized pyrrhotite with assistance of magnetite, which was then precipitated in the form of Cr (OH)3 and Cr2O3 in the aqueous solution. The orthogonal experiment was designed to explore the influences of magnetite particle size, adding dosage, and pH value of wastewater on the synergistic effect between pyrrhotite and magnetite in the process of chromium removal from the aqueous solution. It was found that influences of these three factors was reduced in following order from the pH value of aqueous solution, to the particle size of magnetite, and to the dosage of added magnetite. The optimal condition for removal of Cr(Ⅵ) using pyrrhotite synergistically enhanced by magnetite was given as pH value of 3 for the solution, particle size of 7-150 μm for the magnetite, and the magnetite/pyrrhotite rate of 40%. It is concluded that the synergy between these two minerals should include (1) the inhibition of magnetite on the agglomeration of pyrrhotite in aqueous solution and (2) the fixation of surficial Fe (Ⅲ) of magnetite on the released H2S from pyrrhotite in solution under acidic condition.

Keywords: Magnetite; pyrrhotite; hexavalent chromium; synergistic effect

ACTA MINERALOGICA SINICA Vol. 41, No.2, 2021, page 120-126