Research trends of heavy metal removal from aqueous environments

Heavy metals are a threat against human health. During the last century, with increased industrial activities, many water resources have been contaminated by heavy metals. Meanwhile the number of scientific studies about removing these toxic substances from aqueous environments has increased exponentially. According to bibliometric analysis the number of articles from 2000 to 2019 experienced a 1700% growth rate. China, India and the United States have published the greatest number of top-cited articles on the topic, with China in first place by a large margin. Six clusters of papers (by topic) were identified. From among the processes such as adsorption, membrane filtration, and ion exchange, adsorption has the lion's share of the investigations. Technical and efficiency considerations, as well as environmental impact and cost-effectiveness, were chosen as criteria to compare different methods. According to life cycle assessment, adsorption has the least amount of negative environmental effects compared to other trending methods such as membrane filtration and ion exchange. From a financial viewpoint, utilizing biosorbents and biochars for adsorption are the best options. Unlike other methods which depend on pretreatment processes and have a high energy demand, these sorbents are cost-effective and exhibit acceptable performance.