Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Ruizeng Liu,Dianwen Liu,Zhicheng Liu,Yunwei Wang,Bin Pei,Jialei Li

doi:10.3390/min10040370

Abstract

Sulfidization is required in the amine flotation of smithsonite; however, the sulfidization mechanism of smithsonite is still not fully understood. In this work, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were used to characterize sulfidized and unsulfidized smithsonite. The XPS and UV–vis DRS analyses showed that smithsonite sulfidization is a transformation of ZnCO3 to ZnS on the smithsonite surfaces. However, this transformation is localized, resulting in the coexistence of ZnCO3 and ZnS or in the formation of ZnS island structures on the sulfidized smithsonite surfaces. AFM height imaging showed that sulfidization can substantially change the surface morphology of smithsonite; in addition, AFM phase imaging demonstrated that sulfidization occurs locally on the smithsonite surfaces. Based on our findings, it can be concluded that smithsonite sulfidization is clearly a heterogeneous solid–liquid reaction in which the solid product attaches at the surfaces of unreacted smithsonite. Smithsonite sulfidization involves heterogeneous nucleation and growth of ZnS nuclei. Moreover, the ZnS might nucleate and grow preferentially in the regions with high reactivity, which might account for the formation of ZnS island structures. In addition, sphalerite-structured ZnS is more likely to be the sulfidization product of smithsonite under flotation-relevantconditions, as also demonstrated by the results of our UV–vis DRS analyses. The results of this study can provide deeper insights into the sulfidization mechanism of smithsonite.

Highlights

With the exhaustion of zinc sulfide resources, nonsulfide deposits are increasing in economic importance
The X-ray diffraction (XRD) pattern (Figure 1a) of the powder sample could match the standard pattern for smithsonite ZnCO3 (JCPDS No 08-0449), and no impurity peaks could be observed
The flotation recovery of unsulfidized smithsonite gradually increased with increasing DDA concentration; the desired flotation performance could not

Summary

Introduction

With the exhaustion of zinc sulfide resources, nonsulfide deposits are increasing in economic importance. Many flotation methods employed for recovering zinc oxide minerals have been studied and applied, which involves pre-sulfidization or direct flotation using some collectors such as amines, xanthates, mercaptans, fatty acids and chelating agents [5]. Oxide minerals are well known to not floatas as their sulfide counterparts. In this regard, sulfidization flotation is widely used on an industrial scale for the treatment of zinc oxide ores. The sulfidization process converts the surface of oxide minerals into a sulfide surface. This process involves the dissolution, adsorption and chemical and/or electrochemical reactions [6]. Amines and xanthates can be used for the flotation of the zinc oxide minerals. Further activation using metal ions such as Cu2+ and

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