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Arsenic Toxicity in Water-Soil-Plant System An Alarming Scenario and Possibility of Bioremediation
Published in Amitava Rakshit, Manoj Parihar, Binoy Sarkar, Harikesh B. Singh, Leonardo Fernandes Fraceto, Bioremediation Science From Theory to Practice, 2021
Ganesh Chandra Banik, Shovik Deb, Surajit Khalko, Ashok Chaudhury, Parimat Panda, Anarul Hogue
The geogenic arsenic contamination in soil and aquatic systems has primarily been derived from volcanic eruption and by release of arsenic containing minerals. Arsenic is present in almost all the geological substances with varying degree of concentration. The average concentration of arsenic is 1.5 to 2.0 mg kg-1 in the continental Earth’s crust, with presence of 245 arsenic bearing minerals. These minerals are mostly sulphide-containing ores of copper, nickel, lead, cobalt, zinc, gold or other base metals. The most predominant sulphide ores of arsenic include arsenopyrite (FeAsS), realgar (AS4S4) and orpiment (As2S3). Arsenopyrite (FeAsS) is the most abundant arsenic containing mineral, which exists in anaerobic environments as well as in the crystal lattice structure of various sulphide minerals, as the substitute of sulphur. Arsenolite (As2O3) is the oxidized form of arsenic present in soil while common reduced forms are orpiment (As2S3) and realgar (As4S4). The dissolution of arsenic containing minerals was observed to follow the order: native-arsenic > arsenolite > orpiment > realgar > arsenopyrite > tennantite The release of arsenic in soil and groundwater in deltaic and alluvial plains is mainly attributed to dissolution and desorption of naturally occurring arsenic bearing minerals followed by subsequent leaching and runoff. The geogenic arsenic contamination in soil and groundwater has been observed in different parts of the globe, and the Ganga-Brahmaputra-Meghna fluvial plains of West Bengal, India and adjacent Bangladesh are the typical examples of it.
Arsenic residues from historic gold extraction, Snowy River, Westland, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Arsenolite is much less dispersed than at the nearby Prohibition site where the roaster distributed airborne As over several square kilometres, including the town of Waiuta. Arsenolite is the most soluble and potentially toxic mineral on the site, and some high levels of total As (>70 wt%) principally reflect local accumulations of arsenolite. Other high-As spots on the site reflect accumulations of scorodite and Ca-bearing arsenates. The latter minerals are volumetrically minor but are relatively soluble. In contrast, scorodite is the least soluble oxidised As mineral, and is the most common mineral around the site. Dissolution of As is apparently common in the site, with widespread formation of As-bearing cements and efflorescences. Despite this localised mobility of As, little As is leaving the site in solution, and the Snowy River downstream of the site has low dissolved As concentrations (typically <0.02 mg/L). The Snowy River site is being progressively colonised by forest on its margins, and grasses, mosses, and lichens in the main processing area (Figures 6A, 7A, and 8A,B), and this vegetation partly covers As-rich substrates. However, some high-As patches remain exposed, especially immediately downslope of the cyanide tanks (Figures 7A and 8A,B), and some acidic patches near to the sulphide concentration area (Figure 4A).
The Fate of the Arsenic Species in the Pressure Oxidation of Refractory Gold Ores: Practical and Modelling Aspects
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Wei Sung Ng, Yanhua Liu, Qiankun Wang, Miao Chen
Arsenic oxides in nature commonly take the form of arsenic trioxide as arsenolite (As4O6) or claudetite (As2O3) and occur primarily through the weathering and oxidation of realgar and orpiment (Đorđević et al. 2019). Other forms of arsenic oxides, such as arsenic dioxide (As2O4) and pentoxide (As2O5), rarely occur readily in nature. Due to the conditions of its formation, it is rare for arsenic oxides to be present in gold-bearing sulfide deposits in more than trace quantities.