Removal of Heavy Metal Ions from Water and Wastewaters by Sulfur-Containing Precipitation Agents
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Removal of Heavy Metal Ions from Water and Wastewaters by Sulfur-Containing Precipitation Agents Alina Pohl
Received: 6 March 2020 / Accepted: 14 September 2020 # The Author(s) 2020
Abstract Restrictive requirements for maximum concentrations of metals introduced into the environment lead to search for effective methods of their removal. Chemical precipitation using hydroxides or sulfides is one of the most commonly used methods for removing metals from water and wastewater. The process is simple and inexpensive. However, during metal hydroxide precipitation, large amounts of solids are formed. As a result, metal hydroxide is getting amphoteric and it can go back into the solution. On the other hand, use of sulfides is characterized by lower solubility compared with that of metal hydroxides, so a higher degree of metal reduction can be achieved in a shorter time. Disadvantages of that process are very low solubility of metal sulfides, highly sensitive process to the dosing of the precipitation agent, and the risks of emission of toxic hydrogen sulfide. All these restrictions forced to search for new and effective precipitants. Potassium/sodium thiocarbonate (STC) and 2,4,6-trimercaptotiazine (TMT) are widely used. Dithiocarbamate (DTC) compounds are also used, e.g., sodium dimethyldithiocarbamate (SDTC), and ligands for permanent metal binding, e.g., 1,3-benzenediamidoethanethiol (BDETH2), 2,6-pyridinediamidoethanethiol (PyDET), a pyridine-based thiol ligand (DTPY) or ligands with open chains containing many sulfur atoms, using of a tetrahedral bonding arrangement around a central metal atom. The possibility of improving the efficiency of metal A. Pohl (*) Institute of Environmental Engineering, Polish Academy of Sciences in Zabrze, M. Skłodowskiej-Curie 34 Street, 41-819 Zabrze, Poland e-mail: [email protected]
precipitation is obtained by using a higher dose of precipitating agent. However, toxic byproducts are often produced. It is required that the precipitation agents not only effectively remove metal ions from the solution but also effectively bind with dyes or metal complexes. Keywords Metal sulfide precipitation . Chelating agents . Dithiocarbamate compounds . A synthetic chelating ligand
1 Introduction As civilization develops, the level of environmental pollution with heavy metals intensifies. This pollution has an influence on air, water, and soil contamination by dust, industrial gases, sewage, waste, and coal combustion products containing heavy metals (Nocoń et al. 2006; Barbusiński and Nocoń 2011). The persistent nature of these non-biodegradable pollutants is very dangerous. They tend to accumulate in living organisms. After entering the food chain, they undergo biomagnification processes and finally accumulate in the human body. Heavy metals are classified as substances that pose a particular threat to human health due to their possible toxic or carcinogenic effects (Barakat 2011; Fu and Wang 2011). As a result of many industrial processes, sewage is generated, and it contains a number
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