Anode electrolysis of sulfides.

Traditional sulfide metallurgy produces harmful sulfur dioxide and is energy intensive. To this end, we develop an anode electrolysis approach in molten salt by which sulfide is electrochemically split into sulfur gas at a graphite inert anode while releasing metal ions that diffuse toward and are deposited at the cathode. The anodic splitting dictates the "sulfide-to-metal ion and sulfur gas" conversion that makes the reaction recur continuously. Using this approach, Cu2S is converted to sulfur gas and Cu in molten LiCl-KCl at 500 °C with a current efficiency of 99% and energy consumption of 0.420 kWh/kg-Cu (only considering the electricity for electrolysis). Besides Cu2S, the anode electrolysis can extract Cu from Cu matte that is an intermediate product from the traditional sulfide smelting process. More broadly, Fe, Ni, Pb, and Sb are extracted from FeS, CuFeS2, NiS, PbS, and Sb2S3, providing a general electrochemical method for sulfide metallurgy.

Purification and preparation of pure SiC with silicon cutting waste.

Recycling silicon cutting waste (SCW) plays a pivotal role in reducing environmental impact and enhancing resource efficiency within the semiconductor industry. Herein SCW was utilized to prepare SiC and ultrasound-assisted leaching was investigated to purify the obtained SiC and the leaching factors were optimized. The mixed acids of HF/H2SO4 works efficiently on the removal of Fe and SiO2 due to that HF can react with SiO2 and Si and then expose the Fe to H+. The assistance of ultrasound can greatly improve the leaching of Fe, accelerate the leaching rate, and lower the leaching temperature. The optimal leaching conditions are HF-H2SO4 ratio of 1:3, acid concentration of 3 mol/L, temperature of 50 °C, ultrasonic frequency of 45 kHz and power of 210 W, and stirring speed of 300 rpm. The optimal leaching ratio of Fe is 99.38%. Kinetic analysis shows that the leaching process fits the chemical reaction-controlled model.

Preparation of Al-Si alloys with silicon cutting waste from diamond wire sawing process.

Large amounts of silicon cutting waste (SCW) are generated during Si wafers producing process. In this paper, SCW was mixed with Al powder to prepare Al-Si alloys by a one-step smelting process in corundum crucibles. The influences of smelting temperature (1000 °C, 1200 °C and 1500 °C) on the products of each zone (surface layer zone, loose granular zone and blocky products zone) were investigated. Al-Si alloys in the form of granular and blocky were prepared and the blocky Al-Si alloys mainly concentrated in the blocky products zone. The increase of smelting temperature can promote the aggregation of Al-Si alloy particles. The yields of Al-Si alloy blocks obtained at 1000 °C, 1200 °C and 1500 °C were 0%, 58% and 69%, respectively. The Si contents of Al-Si alloy blocks at 1200 °C and 1500 °C were 15.8 wt% and 17.1 wt% respectively. After compacting the raw materials, the yields of the blocky Al-Si alloys obtained at 1000 °C, 1200 °C and 1500 °C were increased to 65%, 72% and 79% and the corresponding Si contents of the blocky Al-Si alloys were increased to 16.0 wt%, 16.5 wt% and 17.3 wt% respectively. The reaction mechanism of the alloying process was also investigated.

Nucleation and growth mechanism of a nanosheet-structured NiCoSe2 layer prepared by electrodeposition.

Ni-Co-Se layers have attracted a great deal of attention in the field of solar cells, electrocatalyst water splitting and supercapacitors. Electrodeposition is a simple, convenient and low-cost way to obtain Ni-Co-Se layers. However, until now, the electrochemical kinetics of the Ni-Co-Se system, including its growth and nucleation mechanisms, are still unclear. In present work a NiCoSe2 layer with a nanosheet structure was electrodeposited in a chloride bath. The electrochemical mechanisms of the Ni-Co-Se system were also studied. It is noted that the electrochemical kinetics of Ni-Co-Se electrodeposition can be influenced by both temperature and electrode material; however, temperature does not change the progressive nucleation process and mixed controlled growth mechanism of Ni-Co-Se. The diffusion coefficient D and charge-transfer coefficient α of the Ni-Co-Se system were calculated. The values of D obtained by cyclic voltammogram and chromoamperometry are close to each other at both 20 and 50 °C, respectively, and increase with the increase of temperature. Moreover, the activation energy E a was also calculated. Specially, a uniform 3D network-structure NiCoSe2 layer was electrodeposited on ITO glass at -0.9 V and 40 âˆ¼ 60 °C. The increased overpotential during deposition makes the NiCoSe2 layer more easily gather together; however, there is no significant effect on the surface morphology of the NiCoSe2 layer when the temperature is between 40 and 60 °C.

Recovery and reutilization of high-quality boron carbide from sapphire wafer grinding-waste.

Considerable amounts of high-quality boron carbide (B4C) are discarded as J240 sapphire-wafer grinding waste (J240-W), which can be mostly recovered and reutilized after purification for environmental protection. This paper has developed a feasibility method that simultaneously removes the alumina (Al2O3) and iron (Fe) impurities from J240-W with microwave-assisted acid leaching strategy. The influence factors on the Al2O3 leaching ratio, such as leaching temperature, sulfuric acid concentration, liquid-solid ratio and time, have been investigated and optimized. For comparison, the leaching of Al2O3 with conventional and ultrasound-assisted methods has also been performed. The result indicates that the Al2O3 leaching ratio at 80 °C with microwave assistance is 68.95%, much higher than that of conventional (23.66%) and ultrasound (53.13%) methods. Attributed to the unique heating mode of microwave, the Al2O3 leaching ratio can rise to 95.28% at optimum condition, while the content of purified B4C can reach to 98.22% with the residual Al2O3 and Fe fall to 0.26% and 0.12%, respectively. The recovered B4C with high purity and suitable particle size can be reutilized to manufacture W5 abrasive and W0.5 armor material, which is beneficial for environmental protection and resources reutilization.

Mechanisms of the Ammonium Sulfate Roasting of Spent Lithium-Ion Batteries.

Ammonium sulfate ((NH4)2SO4) assisted roasting has been proven to be an effective way to convert spent lithium-ion battery cathodes to water-soluble salts. Herein, thermogravimetric (TG) experiments are performed to analyze the mechanism of the sulfation conversion process. First, the reaction activation energies of the sulfate-assisted roasting are 88.87 and 95.27 kJ mol-1, which are calculated by Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods, respectively. Then, nucleation and growth are determined and verified as the sulfation reaction model by the Satava-Sesták method. Finally, sub-reactions of the sulfation process are investigated and reaction controlling mechanisms are determined by the contribution of sub-reaction. Based on the thermogravimetric analysis, the phase boundary reaction is found to dominate in the initial step of the roasting process (α < 0.6) while the nucleation reaction controlls the following step (α > 0.6), agreeing well with changing trend of activation energy. Overall, thermogravimetric analysis is a general way to study the mechanism of the various roasting processes.

NaOH-assisted low-temperature roasting to recover spent LiFePO4 batteries.

Decreasing the operating temperature of pyrometallurgical methods for recycling spent lithium-ion batteries (LIBs) is key to reducing energy consumption and cost. Herein, a NaOH-assisted low-temperature roasting approach is proposed to recover spent LiFePO4. During roasting, NaOH acts as an oxidizing agent to oxidize Fe (II) to Fe3O4 at 150°C, thus collapsing its stable olivine structure while PO43- capturing Li+ and Na+ to form Li2NaPO4 and LiNa5(PO4)2. The obtained Fe3O4 is then separated, and the resulting Li salt can be further recovered as Li3PO4 with a Li recovery efficiency of 96.7 % and a purity of 99.9 %. Economic and environmental analysis based on the EverBatt model shows that this low-temperature strategy reduces energy consumption and greenhouse gas (GHG) emissions, thus increasing the potential profit. Overall, NaOH-assisted low-temperature roasting is a prospective strategy that broadens the application of NaOH as an oxidant and opens up a new avenue for decreasing the temperature of recovering spent LiFePO4 by pyrometallurgy.

Recycling of silicon from silicon cutting waste by Al-Si alloying in cryolite media and its mechanism analysis.

More than 40% of the crystalline silicon has been wasted as silicon cutting waste (SCW) during the wafer production process. This waste not only leads to resource wastage but also causes environmental burden. In this paper, SCW produced by the diamond-wire sawing process was recycled by Al-Si alloying process. Cryolite was introduced to the reaction system to dissolve the SiO2 layer existed on the surface of the Si particles in SCW. Alloys with 12.02 wt% of Si were prepared and the mechanism of the alloying process was investigated in detail. The Si-Al-cryolite system and SiO2-Al-cryolite system were studied individually to analyze the reaction process and transferring behavior of Si and SiO2 in SCW. The SiO2 shell was firstly transformed into Si-O-F ions. Then the Si-O-F ions diffused to the reaction interface by the effect of the concentration gradient and were reduced to Si by the aluminothermic reduction reaction: 4Al (l) + 3SiO2 (dissolved in the melt) = 3Si (Al)+ 2Al2O3 (dissolved in the melt). Then the internal Si particles were released into cryolite after the dissolution of SiO2 and transferred to the reaction interface by the effect of gravity. The influences of the mass ratio of Al/SCW and agitation modes on the Si content of the alloys and the Si recovery ratio in SCW were investigated. With the increase of the mass ratio of Al/SCW from 2.2 to 6.5, the Si recovery ratio in SCW increased from 44.08% to 69.05%, but the silicon content of the alloys decreased from 16.06 wt% to 8.83 wt%. Agitation can effectively improve the smelting effect during smelting by which the silicon content of the alloys and the Si recovery ratio in SCW increased from 12.02 wt% and 64.25% to 13.17 wt% and 69.46%, respectively.

Study on the synthesis of ß-SiC nanoparticles from diamond-wire silicon cutting waste.

Large amounts of silicon have been wasted as silicon cutting waste (SCW) during the silicon wafer production process, which increases the cost of photovoltaic solar cells and causes environmental pollution. In this paper, an innovative approach for producing ß-SiC nanoparticles by using SCW as silicon source and sucrose as carbon source is reported. The synthesized ß-SiC nanoparticles were characterized by XRD, FTIR, SEM, TEM, Raman, PL and DSC. The results showed that ß-SiC nanoparticles were successfully prepared with a particle size ranging from 40 to 50 nm, and have special photoluminescence as well as good thermal stability. The recycling of SCW can not only solve the environmental pollution issue but also benefits the economy.

Recycling of carbonized rice husk for producing high purity silicon by the combination of electric arc smelting and slag refining.

In this study, the combination of electric arc smelting and slag refining was employed to produce high purity silicon from Carbonized rice husk (CRH) and silica sand. CaO-SiO2-CaF2 were selected as the slagging agents. Firstly, the CRH was mixed with silica sand and slagging agents. Secondly, the mixed raw materials were pelletized and then melted in an experimental electric arc furnace. Thirdly, the cooling graphite crucible was dissected and divided into four parts, i.e., the loose granular zone, skull zone, cavity zone and product zone. Samples were taken from these four parts and analyzed to study the silicon producing mechanism. It was found that the silicon was produced mainly in the skull zone, and silicon with a purity of 96.97% was obtained at the product zone. By adding slagging agents during the smelting process, the impurities in silicon, i.e., Fe, Al and P were reduced thoroughly from 2.06%, 1.33%, 0.09% to 1.04%, 0.08%, and 0.04%, respectively. The results indicate that adding slagging agents CaO-SiO2-CaF2 can remove the impurities effectively from silicon. After acid leaching, the purity of the silicon can reach up to 99.9%.

Influencing factors and kinetics analysis on the leaching of iron from boron carbide waste-scrap with ultrasound-assisted method.

In this paper, the ultrasound-assisted leaching of iron from boron carbide waste-scrap was investigated and the optimization of different influencing factors had also been performed. The factors investigated were acid concentration, liquid-solid ratio, leaching temperature, ultrasonic power and frequency. The leaching of iron with conventional method at various temperatures was also performed. The results show the maximum iron leaching ratios are 87.4%, 94.5% for 80min-leaching with conventional method and 50min-leaching with ultrasound assistance, respectively. The leaching of waste-scrap with conventional method fits the chemical reaction-controlled model. The leaching with ultrasound assistance fits chemical reaction-controlled model, diffusion-controlled model for the first stage and second stage, respectively. The assistance of ultrasound can greatly improve the iron leaching ratio, accelerate the leaching rate, shorten leaching time and lower the residual iron, comparing with conventional method. The advantages of ultrasound-assisted leaching were also confirmed by the SEM-EDS analysis and elemental analysis of the raw material and leached solid samples.