Preparation of Monoclinic Pyrrhotite by Thermal Decomposition of Jarosite Residues and Its Heavy Metal Removal Performance

Cuimin Xu,Tianhu Chen,Fan Xu,Hanlin Wang,Yuefei Zhou,Shuchuan Peng,Qiaoqin Xie

doi:10.3390/min11030267

Abstract

Jarosite residues produced by zinc hydrometallurgical processing are hazardous solid wastes. In this study, monoclinic pyrrhotite (M-Po) was prepared by the pyrolysis of jarosite residues in H2S atmosphere. The influence of gas speed, reaction temperature, and time was considered. The mineral phase, microstructure, and elemental valence of the solids before and after pyrolysis were analyzed using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The performances of the prepared M-Po on the removal of Zn and Pb from aqueous solution were evaluated. The results show M-Po to be the sole product at the reaction temperatures of 550 to 575 °C. Most of the M-Po particles are at the nanometer scale and display xenomorphic morphology. The phase evolution process during pyrolysis is suggested as jarosite → hematite/magnetite → pyrite → pyrite+M-Po → M-Po+hexagonal pyrrhotite (H-Po) → H-Po. The formation rate, crystallinity, and surface microtexture of M-Po are controlled by reaction temperature and time. Incomplete sulfidation may produce coarse particles with core–shell (where the core is oxide and the shell is sulfide) and triple-layer (where the core is sulfate, the interlayer is oxide, and the shell is sulfide) structures. M-Po produced at 575 °C exhibits an excellent heavy metal removal ability, which has adsorption capacities of 25 mg/g for Zn and 100 mg/g for Pb at 25 °C and pH ranges from 5 to 6. This study indicates that high-temperature sulfidation is a novel and efficient method for the treatment and utilization of jarosite residues.

Highlights

Jarosite residues containing mainly iron sulfates and jarosite ((Na, K)Fe3(SO4)2(OH)6) are byproducts of the traditional hydrometallurgy industry [1,2,3]
Diffraction peaks corresponding to natrojarosite were present for experiments at temperatures of
X-ray diffraction (XRD) results show that the lowest transformation temperature of natrojarosite to iron sulfide is in the range of 200–300 ◦C

Summary

Introduction

Jarosite residues containing mainly iron sulfates and jarosite ((Na, K)Fe3(SO4)2(OH)6) are byproducts of the traditional hydrometallurgy industry [1,2,3]. In addition to Fe and S, jarosite residues contain considerable trace elements, such as As, Cd, Cu, Pb, Zn, In, Co, Ge, and Ag, which are originally involved in the raw zinc ores [4,5]. Under natural conditions, these heavy metals are leached from jarosite residues and dispersed into rivers, soils, and other environments, threatening the health of wildlife. In many countries, jarosite residues are required to be stored in specific installations for safety [6,7] Though effective, this temporary method has its shortcomings. Some comprehensive utilization proposals that aim to reuse jarosite and recover key metals are provided

Objectives

Methods

Results

Conclusion