Utilization of Lead Slag as In Situ Iron Source for Arsenic Removal by Forming Iron Arsenate

Application of dirty-acid wastewater treatment technology in non-ferrous metal smelting industry: Retrospect and prospect

Dirty-acid wastewater (DW) originating from the non-ferrous metal smelting industry is characterized by a high concentration of H2SO4 and As. During the chemical precipitation treatment, a significant volume of arsenic-containing slag is generated, leading to elevated treatment expenses. The imperative to address DW with methods that are cost-effective, highly efficient, and safe is underscored. This paper conducts a comprehensive analysis of three typical methods to DW treatment, encompassing technical principles, industrial application flow charts, research advancements, arsenic residual treatment, and economic considerations. Notably, the sulfide method emerges as a focal point due to its minimal production of arsenic residue and the associated lowest overall treatment costs. Moreover, in response to increasingly stringent environmental protection policies targeting new pollutants and carbon emissions reduction, the paper explores the evolving trends in DW treatment. These trends encompass rare metal and sulfuric acid recycling, cost-effective H2S production methods, and strategies for reducing, safely disposing of, and harnessing resources from arsenic residue.

Deep-dive into iron-based co-precipitation of arsenic: A review of mechanisms derived from synchrotron techniques and implications for groundwater treatment

The co-precipitation of Fe(III) (oxyhydr)oxides with arsenic (As) is one of the most widespread approaches to treat As-contaminated groundwater in both low- and high-income settings. Fe-based co-precipitation of As occurs in a variety of conventional and decentralized treatment schemes, including aeration and sand filtration, ferric chloride addition and technologies based on controlled corrosion of Fe(0) (i.e., electrocoagulation). Despite its ease of deployment, Fe-based co-precipitation of As entails a complex series of chemical reactions that often occur simultaneously, including electron-transfer reactions, mineral nucleation, crystal growth, and As sorption. In recent years, the growing use of sophisticated synchrotron-based characterization techniques in water treatment research has generated new detailed and mechanistic insights into the reactions that govern As removal efficiency. The purpose of this critical review is to synthesize the current understanding of the molecular-scale reaction pathways of As co-precipitation with Fe(III), where the source of Fe(III) can be ferric chloride solutions or oxidized Fe(II) sourced from natural Fe(II) in groundwater, ferrous salts or controlled Fe(0) corrosion. We draw primarily on the mechanistic knowledge gained from spectroscopic and nano-scale investigations. We begin by describing the least complex reactions relevant in these conditions (Fe(II) oxidation, Fe(III) polymerization, As sorption in single-solute systems) and build to multi-solute systems containing common groundwater ions that can alter the pathways of As uptake during Fe(III) co-precipitation (Ca, Mg bivalent cations; P, Si oxyanions). We conclude the review by providing a perspective on critical knowledge gaps remaining in this field and new research directions that can further improve the understanding of As removal via Fe(III) co-precipitation.

Arsenic methylation behavior and microbial regulation mechanisms in landfill leachate saturated zones

Arsenic (As) is a potential contaminant in landfill. As methylation has been considered as a detoxification mechanism to address this problem. In this study, microcosm incubation was used to simulate leachate saturation zone (LSZ) and other landfill zones scenarios to explore the As methylation behavior. The As methylation rate of LSZ is 11.75%, which is slightly higher than that of other zone of landfill (10.87%). However, the difference was greatly increased by the addition of moderate content of As(III), with values of 29.25% in LSZ and 4.61% in other zones. The microbial community structure varied greatly between zones and a higher abundance of arsM was observed in the LSZ, which enhanced As methylation. Based on the annotated As functional genes from the KEGG database, the microbial As methylated pathway was summarized. Higher relative abundances of gst and arsC promoted the formation of more trivalent As substrates, stimulating the methylation behavior for As detoxification in the LSZ. According to microbial arsM contribution analysis, unclassified_p__Gemmatimonadetes, unclassified_p__Actinobacteria, unclassified_o_Hydrogenophilales, and Intrasporangium were the primary As methylation bacteria in the LSZ, while unclassified_f__Chitinophagaceae and unclassified_c_Gammaproteobacteria were the primary contributors in other landfill zones. These results highlight the specific As methylation process in the LSZ, and these insights could improve the control of As contamination in landfill sites.