The Study Of Thermal Decomposition Mechanism Of Heavy Metal Xanthate

Alkyl xanthate, a typical flotation reagent, gets more and more attentions in otherscientific research fields in recent years, especially in the system of metal sulfidenanomaterials prepared by using single source precursor. However, there are someshortcomings in this process, for example, expensive reagent, high reactiontemperature, complicated synthetic procedures. In addition, there is not a generalagreement on the reaction mechanism in the process of the preparation. Therefore, theaim of my study is to find out the xanthate–metal sulfide reaction mechanism and thetransfornmation mechanisms of from metal xanthates to metal sulfide. The mainresearch contents and results are as follows:1. ZnS powder was prepared by calcinations of the precipitates ofZn(NO3)2·6H2O and Na2S·9H2O in aqeous solution, The specific surface area of thesample is determinedusing a surface area analyzer to be98.94m2/g. The crystalstructure and particle size of sample was characterized using XRD technique. Theadsorption experiments of xanthate in the presence and absence of copper and leadions were carried out to evaluate the activation effect. The results showed that thesurface hydrophobicity and the adsorbing capability of ZnS on xanthate after activatedby Cu2+and Pb2+were substantially improved. The contact angle increased by86.8%and31.5%, and the adsorption quantity increased by95.5%and53.3%, respectively.The activation process was also discussed and we believed that the mechanism was acombined process of ion exchange and redox reactions.2. ZnS nanoparticles of a few nanometers in size were prepared by thermolysisof a single source precursor of metal xanthates with different reacting time in anammonia solution. The particle size and crystallinity of these ZnS nanoparticles werecharacterized by X-ray powder diffractometry techniques. The decompositionmechanism of ZnX2is studied using FTIR and UV-vis spectra in combination withGC-MS photometry. The results show that cubic and hexagonal ZnS nanoparticlescan be prepared by thermolysis of ZnX2in an aqueous solution of ammonia attemperature as low as90℃. The decomposition mechanism is found to be a simplenucleophilic addition reaction with reaction products of MS nanoparticles, alkanols,carbonyl sulfide and dithantogen. The olefin, the main reaction product of Chugaevreaction, is not detected in this process, which suggests that Chugaev reaction is notapplicable in explaining the transformation mechanism of ZnX2to ZnS. 3. ZnS quantum dots (QDs) capped with n-butylxanthate (n-BX) are synthesisedby a simple solvothermal route using ethanol zinc and potassium n-butylxanthate asthe precursors. The nanoparticles obtained show quantum size effects in the opticalabsorption spectra and the photoluminescence shows an emission maximum that ischaracteristically red shifted in relation to the band edge. The X-ray diffraction (XRD)pattern shows the material to be cubic with a calculated particle size (from theScherrer equation) of range about2.1nm. The size of the particles is confirmed by thetransmission electron microscope (TEM) image, which shows well-defined, sphericalparticles with an average size of4~6nm. Moreover, the synthesis process of the ZnSQDs is also discussed.