Study Of Prepared Tellurium Film With Spectral Selectivity And New Process To Recover Of Tellurium From Lead-rich Tellurium Slag

Many copper smelting enterprises in China usually use alkaline leaching-removing impurities by sodium sulfide-neutralization-electrolysis process to recover tellurium from the lead tellurium slag resulting from the treatment of copper anodes slime. This process has drawbacks such as long flowsheet, the tellurium recovery yield being low, the product quality being unstable and less flexibility to raw material. The research goal of the dissertation is to find a new process with many advantages including adaption to chemical composition change of the slag, short process, simpley operation, high tellurium recovery ratio and stable product quality.In this study, on the basis of the summarizesing of predecessor's research results, a new process for the recovery of tellurium from lead tellurium slag was developed through thermodynamic computation and the experimental study. The new process is consist of sulfuric acid leaching--reduction of Te by sodium sulfite(or sulfur dioxide)-Se removing from raw tellurium by sodium sulfite-purification of Te by hydrochloric acid-powdered tellurium. Large-scale experiment was conducted in a factory. The experiment result has confirmed the technical process is feasible, technological conditions are suitable. The experiment showed the optimum process parameters of sulfuric acid leaching were as follows: H₂SO₄ concentration 5 mol/L, reaction time 240min, reaction temperature 80℃, liquid-to-solid rato 6 : 1, particle size of lead tellurium slag≤0.124mm (-120 mesh) The optimum process parameters of reduction of Te by sodium sulfite in sulfuric acid solution were as follows: mass ratio Na₂SO₃/Te=10, NaCl/Te=4, reaction temperature 80℃, reaction time 60min. The optimum process parameters of reduction of Te by SO₂ in sulfuric acid solution were SO₂/Te=5, NaCl/Te=6, reaction temperature 80℃, reaction time 40min. The suitable condition for removing of Se from raw powdered tellurium by sodium sulfite were liquid-to-solid 10 : 1, Na₂SO₃ concentration 1 mol·L-1, reaction temperature≥95℃, reaction time 60min. A total tellurium recovery ratio of higher than 90% and commercial grade tellurium powder with purity 99.669% was obtained from the new process. Our process extraction of Te from lead-rich tellurium sediment has many advantages such as applicabiling to stag chemical composition change, short process, easy control, low production cost and stable product quality.The feasibility of preparing high-purity tellurium by chemical of impurity was confirmed through thermodynamic computation. The entire chemical process of preparing high-purity tellurium containing 99.99～99.999% Te with commercial grade tellurium powder has confirmed through the study. The process consists of tellurium powder-eliminating impurity by HNO3 oxidation-NaOH dissolving-eliminating impurity by Na2S-removing of Se by SO2 reduction-high purity tellurium obtained by reduction with SO2. The experiment showed the optimum process parameters of prepared high purity tellurium were as follows: HNO₃ excess coefficient 1.05, pH=11 for eliminating impurity by Na₂S, Na₂S excess coefficient 1.05 at reaction temperature 90℃, removing of Se by SO2 reduction at HCt concentration 6mol/L and reaction temperature 85℃, high purity tellurium preparing by reduction with SO₂ at HCl concentration 1.5mol/L and reaction temperature 85℃. Under above condition, high purity tellurium with purity of high than 99.9992% and impurity of low than 0.0008% was directly obtained from our process. The recovery yield of tellurium obtained from entire chemical process is higher than 90%.In this paper, spectral selectivity tellurium films was deposited onto polyethylene foil by chemical vapor deposition (CVD) method with self-made equipment and the feed of high pure tellurium came from the above entire chemical process. The structure, surface morphology and optical properties of the tellurium films were investigated with powder X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive X-ray (EDX), ultraviolet-visible-near infrared ray Spectrophotometer (UV-Vis-NIR) and FT-infrared ray spectrophotometer (FTIR). The result showed the tellurium films deposited onto polyethylene foil and permanganate (KMnO₄) surface-treated polyethylene foil had completely different deposition speed, structure and optical properties. After the treatment the polyethylene foil becomes hydrophilic. Higher nucleation rate and density, better adhesion and high deposition speed of the tellurium films are obtained by permanganate (KMnO₄) surface treatment of polyethylene. The tellurium films texture change from (100) texture to (011), (102) and (003) texture, but the reflectance of tellurium film in the UV/Vis/NIR region and the transmission of tellurium film in the 8-13μm region are decreased. The result also showed deposition speed and crystallite size of the tellurium film rise with the increasing temperature of substrate, but the adhesion decrease with the increasing temperature, so the deposition temperature of substrate can not exceed 60℃. The thickness and the surface roughness of Te film increases with the increasing deposition time, which leads to decrease of the reflectance and the transmission of tellurium film in the UV/Vis/NIR and IR region, respectively. The deposition speed, surface evenness, nucleation rate and density of tellurium film rise with the increasing concentration of H2Te in the mixture gas, which leads to increase in the reflectance and decrease in the absorption of tellurium film in the UV/Vis/NIR region, respectively. The progresses of nucleation and growth of tellurium thin film are studied by SEM and EDX, and also discussed from the point of view of kinetics and thermodynamics. The result indicated that spontaneous nucleation of tellurium occurs on the bare polyethylene substrate and non-spontaneous nucleation on treated polyethylene substrate. The nucleation occurs in the island growth mode on the treated polyethylene substrate. When the critical state of the island is reached the phase transformation occurs, and solid tellurium film forms. After the solid tellurium film swallows up the island, the tellurium film enters the layer-by-layer growth period.