Recovery of valuable and toxic metals from crystalline-Si modules
Valuable and toxic metals including Ag, Pb, Sn and Cu can be recovered from end-of-life Si solar modules. This study presents the recovery of Ag, Pb, Sn and Cu from a simulated leach solution of crystalline-Si modules. 11.4% HNO3 is used as the leach solution. Ag, Pb, Sn and Cu pellets are dissolved in the solution to simulate the metals from front contacts and soldered wires in Si modules. Sn precipitates in the solution as SnO2, which can be separated by filtration or sedimentation. Voltammetry reveals the reduction potentials for Ag and Cu. It is demonstrated that 3-electrode sequential electrowinning can extract Ag and Cu one by one from the solution. The recovery rates of Ag and Cu are 74% and 83%, respectively. Toxic Pb is deposited on the anode as PbO2 during Cu recovery. The purity of the extracted metals is above 99%.
Leaching of lead from solder material of waste printed circuit boards (PCBs)
Abstract Present work is focused on the selective leaching of lead from the soldering material present on the outer layer i.e. epoxy resin of waste PCBs, liberated through a novel pre-treatment technique of organic swelling using n-methyl-2-pyrrolidone. Nitric acid was found as a suitable leachant to dissolve lead. Initially, the effect of temperature, S:L ratio, leaching time and acid concentration on leaching of lead was investigated using fresh solder material containing 47.36% lead and remaining tin. With 0.2 M HNO 3 at S:L ratio 1:100 (g/mL) and temperature 90 °C, 99.99% lead was leached in 120 min. Leaching kinetics followed 1 − (1 − X) 1/3  = K c t i.e. chemically controlled reaction model with activation energy 26.94 kJ/mol. Validation of lead leaching from solder of liberated epoxy resin of swelled PCBs indicates that 99.99% of lead could be leached out at 90 °C with 0.2 M HNO 3 in 45 min. Tin left in the residue of the liberated resin was further leached with 3.5 M HCl at 90 °C for 120 min at S:L ratio 1:20 (g/mL), which dissolve almost 98.74% tin. Then, metal free epoxy resin was washed with water to utilize it or dispose-of safely without affecting the environment.
Terawatt Solar Photovoltaics: Roadblocks and Opportunities
Global power demands are projected to reach 46 terawatts by 2100. Solar photovoltaics has to reach a scale of tens of peak terawatts in order to meet a meaningful portion of the demands. The enormous scale required creates a number of roadblocks for photovoltaic technologies, which are unprecedented in other semiconductor technologies. Some of the roadblocks include scarce raw materials used in today's solar cells, high energy input for silicon solar cells, life-cycle management of solar modules, storage of intermittent solar electricity, and high production/installation costs for solar cells/modules. In this talk an analysis will be presented, as quantitatively as possible, on some of these roadblocks under the best scenarios, i.e. the maximum possible wattage from each of the current commercial cell technologies. It is concluded that without significant technological breakthroughs, the current commercial cell technologies combined would not be able to make a noticeable impact on our energy mix or carbon emissions. Based on this analysis, several strategic R&D directions are identified for a scalable and sustainable solar photovoltaic technology.