Industrial waste utilization method： producing poly-ferric sulfate （PFS） from sodium-jarosite residue

Sodium-jarosite is a type of industrial waste that results from hydrometallurgy and inorganic chemical production. The iron content of jarosite residue may be utilized to produce theoretically the ferrous materials. The difficulty in production of high quality poly-ferric sulfate （PFS） is how to remove impurities contained in jarosite residue. This paper proposes a novel method for disposing sodium-jarosite which can be used to synthesize PFS, a very important reagent for treating waste water. The method consists of a two-step leaching experimental procedures. The first step, pre-leaching process, is to remove impurity metals by strictly controlling the leaching conditions. The acid concentration of acidic water was adjusted according to the content of impurity metals in sodium-jarosite and the leaching temperature was controlled at 25°C. The second step is to decompose sodium-jarosite to provide enough ferric ions for synthesizing PFS, the concentrated sulfuric acid consumption was 0.8 mL·g^-1 sodium-jarosite and the leaching temperature was above 60°C. In the experiment, decomposing iron from sulfate sodium-jarosite can take the place of ferric martials for synthesizing PFS. Results show that the PFS synthesized from sodium-jarosite had a high poly-iron complex Fe4.67（SO4）6（OH）2·20H2O. Further, the PFS product’s specifications satisfied the national standard of China.

A critical review on the recycling of copper and precious metals from waste printed circuit boards using hydrometallurgy

Currently, increasing amounts of end-of-life （EoL） electronic products are being generated due to their reduced life spans and the unavailability of suitable recycling technologies. In particular, waste printed circuit boards （PCBs） have become of global concern with regard to environmental issues because of their high metal and toxic material contents, which are pollutants. There are many environmental threats owed to the disposal of electronic waste; off-gasses, such as dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons, can be generated during thermal treatments. which can cause serious health problems if effective off=gas cleaning systems are not developed and improved. Moreover, heavy metals will dissolve, and release into the ground water from the landfill sites. Such waste PCBs contain precious metals which are of monetary value. Therefore, it is beneficial to recover the metal content and protect the environment from pollution. Hydrometallurgy is a successful technique used worldwide for the recovery of precious metals （especially gold and silver） from ores, concentrates, and waste materials. It is generally preferred over other methods because it can offer high recovery rates at a relatively low cost. This article reviews the recent trends and developments with regard to the recycling of precious metals from waste PCBs through hydrometallurgical techniques, such as leaching and recovery.