Wenyi Yuan

Characterization of Extreme Acidophile Bacteria (Acidithiobacillus ferrooxidans) Bioleaching Copper from Flexible PCB by ICP-AES

In order to improve copper leaching efficiency from the flexible printed circuit board (PCB) by Acidithiobacillus ferrooxidans, it is necessary to quantitatively measure the bacteria bioleaching copper under extreme acidic condition from flexible PCB. The inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is a very accurate way to analyze metals in solution; this paper investigated the optimal conditions for copper bioleaching by Acidithiobacillus ferrooxidans from flexible PCB through ICP-AES. The conditions included particle size of flexible PCB powder, quantity of flexible PCB powder, initial pH of culture medium, bacteria inoculation, bacteria activation time, and quantity of FeSO4·7H2O. Prior to ICP-AES measurement, culture solution was digested by aqua regia. The experimental results demonstrated that flexible PCB contained one main metal (copper); this was associated with the structure of flexible PCB. The optimization conditions were in 50 mL medium, flexible PCB 10 g/L, particle size of flexible PCB 0.42~0.84 mm, culture medium initial pH 2.5, bacteria inoculation 5%, bacteria activation time 5 d, and quantity of FeSO4·7H2O 30 g/L. Under the optimization condition, the leaching rate of copper was 90.10%, which was 42.4% higher than the blank group. For the ICP-AES determination, it reached a conclusion that the best corresponding wavelength (nm) of copper will be 224.7 (nm).

Lead recovery from scrap cathode ray tube funnel glass by hydrothermal sulphidisation

This research focused on the application of the hydrothermal sulphidisation method to separate lead from scrap cathode ray tube funnel glass. Prior to hydrothermal treatment, the cathode ray tube funnel glass was pretreated by mechanical activation. Under hydrothermal conditions, hydroxyl ions (OH–) were generated through an ion exchange reaction between metal ions in mechanically activated funnel glass and water, to accelerate sulphur disproportionation; no additional alkaline compound was needed. Lead contained in funnel glass was converted to lead sulphide with high efficiency. Temperature had a significant effect on the sulphidisation rate of lead in funnel glass, which increased from 25% to 90% as the temperature increased from 100 °C to 300 °C. A sulphidisation rate of 100% was achieved at a duration of 8 h at 300 °C. This process of mechanical activation and hydrothermal sulphidisation is efficient and promising for the treatment of leaded glass.

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

AbstractCurrently, 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.

Improving arsenic mobility concentration from As-polluted soils by the functional strains

Arsenic (As) contamination has become the environment issue of global concern. In China, large area of farmland and the site soil were contaminated by As, which means that suitable remedying methods were urgently needed. Phytoremediation, as one of environment-friendly soil remediation techniques developed in recent years, shows a bright future for the remediation of As contaminated soils. However, phytoremediation efficiency needs to be enhanced further because of low concentration of bio-available As in the soils. A triangle flask culture experiment was carried out to study the effects of functional species, isolated from As-polluted soils, that could improve As mobility from the soil. These species included two bacilli, B1 and B2 (Brevibacillus) and two fungi, F1 (Trichoderma), F2 (Fusarium). They could transform the concentration of As fractionation in the soil sterilized by the method of 60Co-γ ray. Through the experiment, the concentrations of non-specifically-sorbed and specifically-sorbed As fractionation, and pH value of culture solution with inoculated treatment were higher than that with the control. Especially, the concentration of non-specifically-sorbed As fractionation in the treatment-inoculated species was 2 to 6 times higher than that of non-inoculation treatment. Moreover, two bacilli and two fungi could produce IAA, which was conducive to the plant survival when they were jointly used in remedying the As-contaminated soil.

Recycling of Polysilicon Byproduct SiCl4 Dissolved in Ionic Liquids

AbstractSilicon tetrachloride (SiCl4) is one of the primary by-products products of the polysilicon industries, which must also be handled with care, as it is both toxic and reactive. The dissolution of SiCl4 and electrodeposited of Si in ionic liquids (ILs) was investigated. Six kinds of ILs were examined as the solvents; the cations were 1-Butyl-3-methylimidazolium 1-butyl-3-methylimidazolium ([Bmim]+), 1-Hexyl-3-methylimidazolium ([Hmim]+), 1-Octyl-3-methylimidazolium ([Omim]+), N-butyl-3-methylpyridinium ([B3MePy]+), N-hexyl-3-methylpyridinium ([H3MePy]+), N-octyl-3-methylpyridinium ([O3MePy]+); the anion was bis[(trifluoromethyl)sulfonyl]imide ([NTf2]−). The results indicated that a decrease in the solubility of SiCl4 in ILs followed an increase in temperature. The presence of Si-O bonding between the ionic liquid and SiCl4 enhanced the SiCl4 dissolving capacity of in the ILs with anion of [NTf2]−. Longer alkyl chain lengths in the imidazolium and pyridinium cations of the ILs exhibited a better performance in dissolving SiCl4, due to the presence of C-Cl and C-Si formed between the ILs and SiCl4. Si was electrodeposited on a Ti plate under potential of 2.92V, of which a Si weight of up to 28.43 wt% was observed. The deposition product on the electrode is in the coexistence state of Si and SiOx due to the deposition conditions at ordinary temperature and pressure. Graphical AbstractRecycling of Polysilicon Byproduct SiCl4 by dissolution and electrodeposition in Ionic Liquids

Mechanochemical treatment of Cr(VI) contaminated soil using a sodium sulfide coupled solidification/stabilization process

In this research, mechanochemical reduction was carried out to remediate Cr(VI) contaminated soil, and the reduction effectiveness was evaluated by analyzing the corresponding leachable fraction obtained through the toxicity characteristic leaching procedure (TCLP) proposed by the EPA. The results indicated that mechanochemical reduction can efficiently reduce the Cr(VI) concentration in the leachate. Under a milling time of 2 h, milling speed of 500 rpm, ball-to-powder weight ratio of 14 and Na2S dosage of 5%, the Cr(VI) leaching concentration significantly decreased from 663.98 mg L-1 to 0.84 mg L-1, much lower than the regulatory limit of 5 mg L-1. In addition, the significant decrease in Cr(VI) was mainly due to the reduction of Cr(VI) to Cr(III), as supported by X-ray photoelectron spectroscopy (XPS). The mechanochemical reduction with mechanism proposed in this experiment may involve two major processes: solidification and reduction (stabilization).