China 
Africa 
Explore chapters and articles related to this topic
Microbial Processes for Treatment of e-Waste Printed Circuit Boards and Their Mechanisms for Metal(s) Solubilization
Published in Ram Chandra, R.C. Sobti, Microbes for Sustainable Development and Bioremediation, 2019
Shailesh R. Dave, Asha B. Sodha, Devayani R. Tipre
Cyanide forms a water-soluble complex with gold, and it is responsible for gold extraction. The use of biogenic cyanide provides an alternative, eco-friendly gold extraction process, which can be referred alkaline bioleaching or heterotrophic bioleaching process. HCN is generated by diverse heterotrophic organisms. The enzyme involved for gold recovery is called as HCN synthase. Normally, HCN is produced between the end of an exponential phase and early stationary phase during the growth of C. violaceum and at the beginning of the stationary phase by Pseudomonas. In the case of Chromobacterium, the produced HCN is detoxified during the late stationary phase by transforming it to β-cyanoalanine (Dave et al. 2018, 2016a; Knowles and Bunch 1989; Brandl et al. 2008). The dissolution of gold can be expressed as following anodic (Eq. 8.7) and cathodic (Eq. 8.8) reactions. The overall reaction is known as Elsner’s equation (Eq. 8.9).
Environmental Impact of Gold Mining
Published in Mritunjoy Sengupta, Environmental Impacts of Mining, 2021
The use of liquid mercury in small-scale mining is a serious threat to water quality in many parts of the world. Mercury, when used in the gold extraction process, forms an amalgam and turns into a stable methyl-mercury compound, which when ingested, inhaled, or absorbed by fauna and flora becomes toxic to man and the environment. In Ghana small-scale miners use mercury in the processing of their ore. In most cases, the waste products are dumped into water bodies, which cause bio-accumulation in the bodies of aquatic animals and enter the food chain of human beings. Exposure to mercury can cause kidney problems; disorders of respiratory, central nervous, and cardiovascular systems; loss of memory; psychosis; reproductive problems; and, in some cases, severe complications in children resulting in death. In Ghana, contaminations of surface and groundwater bodies have particularly been experienced in gold mining communities. When chemicals such as the cyanide used in processing the ore leak, spill, or leach from the processing site into nearby water bodies, those can be harmful to humans, aquatic organisms, and wildlife, as a whole. The majority of small-scale surface miners in Ghana wash the waste products from the ore processing into the rivers and other water bodies that serve as sources of clean portable drinking water to the mining communities. Others release mine tailings directly into aquatic habitats. Mine tailings are often toxic and pose serious health threats to plant life, humans, and animals. Research revealed that many mining communities in the western region of Ghana are at risk of health issues from heavily polluted water bodies by small-scale mining activities.
The prospects for an alternative gold leach reagent: Thiourea
Published in Gülhan Özbayoğlu, Çetin Hoşten, M. Ümit Atalay, Cahit Hiçyılmaz, A. İhsan Arol, Mineral Processing on the Verge of the 21st Century, 2017
The latest developments in new gold extraction methods have not only reflected the economic aspects in terms of increased recovery and reduced overall costs, but also the environmental considerations. Thiourea leaching technique has many advantages over the cyanidation process, some of which are: the higher kinetic rates and in consequence a much shorter time of reaction. Thiourea is not restricted by the same toxicity factors as cyanide and finally it has been reported to be affected too much lesser degrees by the presence of some of these cyanidation inhibitors.
Gold extraction from biosolid sludge obtained by sewage treatment
Published in Environmental Technology, 2019
Sara AlKetbi, Hussain Elsayed, Sulaiman Al-Zuhair
Gold is a precious metal, which if found among the heavy metals extracted from the biosolids would make the treatment process more advantageous. A survey of metal concentrations found in the sludge treated in the biosolid treatment facilities of Texas indicated the presence of gold in the biosolids [24]. Gold extraction by potassium cyanide solution is an old method, which is used at a large scale for extracting gold from its ores. After extraction, the extracted gold is precipitated using zinc shavings. Potassium cyanide has a high extraction selectivity for gold, allowing only gold to be extracted leaving behind other metals. However, this technique is not suitable for heavy metal extraction from biomass meant to be used as a fertilizer, because it is more desirable to extract all heavy metals and not only gold. In addition, cyanide is highly poisonous and harmful to the environment. Thiourea has been suggested as an alternative safer solvent [25]. A solution containing 24 g/L of thiourea and 0.6% of Fe3+ was found to be effective, and within 2 h, over 90% of gold was extracted from mobile phone scraps. However, the main disadvantages of this technique are the high cost of the oxidant (ferric ion) and the need for large volumes of reagents [26].