The Separation of Aluminum and Stainless-Steel Scraps Using Vibrating Mixed-Size Ball Bed

Feasibility of gold leaching from waste printed circuit boards with an airlift bioreactor applying the condensed distillers solubles as a microbial nutrient and its recovery by reduction

To improve the bio-cyanide production by Chromobacterium violaceum, an airlift bioreactor was designed, and its performance was evaluated. Condensed distillers solubles, a byproduct of the ethanol production process, served as a nutrient source for C. violaceum. During bacterial cultivation, the produced cyanide was volatilized and captured in a 1M NaOH solution connected to an airlift bioreactor. Through the optimization of the bio-cyanide production process in the bioreactor, a cyanide concentration of 596.4 ± 14.8 mg/L was obtained in the NaOH collector after 8 days, which was utilized to leach Au from waste printed circuit boards (WPCBs). Na2S2O4 was employed in the Au reduction process after Au leaching. Under optimal conditions with a reductant concentration of 1 g/L, a reaction temperature of 60 °C, and pH 11, 99.3 % of Au was recovered within 6 h. Additionally, based on the optimal conditions obtained in this study, a comprehensive economic feasibility assessment for the entire process of Au leaching using bio-cyanide and Au reduction with Na2S2O4 was performed. Calculations indicated that a gross profit of USD 31,248.9 could be achieved per tonne of WPCBs with an Au content of 0.1 %. These findings suggest that bioleaching represents a cost-effective and environmentally friendly alternative to recover Au from WPCBs.

Conventional and recent advances in gravity separation technologies for coal cleaning: A systematic and critical review

"Affordable and clean energy" is enshrined in the UN Sustainable Development Goals (SDGs; #7) because of its importance in supporting the sustainable development of society. As an energy source, coal is widely used because it is abundant and its utilization for electricity and heat generation do not require complex infrastructures and technologies, which makes it ideal for the energy needs of low-income and developing countries. Coal is also essential in steel making (as coke) and cement production and will continue to be on high demand for the foreseeable future. However, coal is naturally found with impurities or gangue minerals like pyrite and quartz that could create by-products (e.g., ash) and various pollutants (e.g., CO₂, NO_X, SO_X). To reduce the environmental impacts of coal during combustion, coal cleaning-a kind of pre-combustion clean coal technology-is essential. Gravity separation, a technique that separates particles based on their differences in density, is widely used in coal cleaning due to the simplicity of its operation, low cost, and high efficiency. In this paper, recent studies (from 2011 to 2020) related to gravity separation for coal cleaning were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 1864 articles were screened after removing duplicates, and after a thorough evaluation 189 articles were reviewed and summarized. Among of conventional separation techniques, dense medium separator (DMS), particularly dense medium cyclone (DMC), is the most popular technologies studied, which could be attributed to the growing challenges of cleaning/processing fine coal-bearing materials. In recent years, most of works focused on the development of dry-type gravity technologies for coal cleaning. Finally, gravity separation challenges and future applications to address problems in environmental pollution and mitigation, waste recycling and reprocessing, circular economy, and mineral processing are discussed.

Leaching of Copper from Waste-Printed Circuit Boards (PCBs) in Sulfate Medium Using Cupric Ion and Oxygen

In the present paper, the leaching of copper from printed circuit boards (PCBs) using sulfuric acid with Cu2+ and O2 is proposed. The effects of various process parameters such as agitation speed, temperature, the type and the flow rate of gas, initial Cu2+ concentration, and pulp density were investigated to examine the dissolution behavior of Cu from PCBs in 1 mol/L sulfuric acid. The kinetic studies were performed using the obtained leaching data. The leaching rate of Cu from PCBs was found to be higher on addition of Cu2+ and O2 to the leachant in comparison with the addition of O2 or both Cu2+ and N2 in the leachant. The leaching efficiency of Cu was found to be increased with increasing agitation speed, temperature, O2 flow rate, and initial Cu2+ concentration and decreasing pulp density. The 96% of Cu leaching efficiency was obtained under the following conditions: sulfuric acid concentration, 1 mol/L; temperature, 90 °C; agitation speed, 600 rpm; pulp density, 1%; initial Cu2+ concentration, 10,000 mg/L; and O2 flow rate, 1000 cc/min. The leaching data and analyses indicate that the Cu leaching from PCBs followed the reaction-controlled model satisfactorily and determined that the activation energy was found to be 23.8 kJ/mol. Therefore, these results indicate that the sulfuric acid solution with Cu2+ and O2 as a mild leach medium without strong oxidants such as HNO3, H2O2, and Fe3+ is valid for Cu leaching from PCBs.

Recent Advancements in Plastic Packaging Recycling: A Mini-Review

Today, the scientific community is facing crucial challenges in delivering a healthier world for future generations. Among these, the quest for circular and sustainable approaches for plastic recycling is one of the most demanding for several reasons. Indeed, the massive use of plastic materials over the last century has generated large amounts of long-lasting waste, which, for much time, has not been object of adequate recovery and disposal politics. Most of this waste is generated by packaging materials. Nevertheless, in the last decade, a new trend imposed by environmental concerns brought this topic under the magnifying glass, as testified by the increasing number of related publications. Several methods have been proposed for the recycling of polymeric plastic materials based on chemical or mechanical methods. A panorama of the most promising studies related to the recycling of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) is given within this review.