Abstract
This review examines a variety of adsorbents and discusses mechanisms, modification methods, recovery and regeneration, and commercial applications. A summary of available researches has been composed by a wide range of potentially low-cost modified adsorbents including activated carbon, natural source adsorbents (clay, bentonite, zeolite, etc.), biosorbents (black gram husk, sugar-beet pectin gels, citrus peels, banana and orange peels, carrot residues, cassava waste, algae, algal, marine green macroalgae, etc.), and byproduct adsorbents (sawdust, lignin, rice husk, rice husk ash, coal fly ash, etc.). From the literature survey, different adsorbents were compared in terms of Zn2+adsorption capacity; also Zn2+adsorption capacity was compared with other metals adsorption. Thus, some of the highest adsorption capacities reported for Zn2+are 168 mg/g powdered waste sludge, 128.8 mg/g dried marine green macroalgae, 73.2 mg/g lignin, 55.82 mg/g cassava waste, and 52.91 mg/g bentonite. Furthermore, modification of adsorbents can improve adsorption capacity. Regeneration cost is important, but if consumption of virgin adsorbent is reduced, then multiple economic, industrial, and environmental benefits can be gained. Finally, the main drawback of the already published Zn2+adsorption researches is that their use is still in the laboratory stage mostly without scale-up, pilot studies, or commercialization.
Highlights
Water is a source of energy and life, millions of people worldwide are suffering from the shortage of clean drinking and fresh water
In Malaysia, the discharge of heavy metals to the water bodies should be stipulated to the limits of standard A and B according to the Environmental Quality (Sewage and Industrial Effluents) Regulations, Environmental Quality Act 1974 [7]
Using plant wastes for wastewater treatment has some of the advantages such as simple technique, requiring little processing, adsorption of heavy metal ions, good adsorption capacity, selective, low-cost, and free availability, and easy regeneration
Summary
Water is a source of energy and life, millions of people worldwide are suffering from the shortage of clean drinking and fresh water. Metal ions in water can occur naturally from anthropogenic sources and from leaching of ore deposits, which mainly include solid waste disposal and industrial effluents. In Malaysia, the discharge of heavy metals to the water bodies should be stipulated to the limits of standard A and B according to the Environmental Quality (Sewage and Industrial Effluents) Regulations, Environmental Quality Act 1974 [7]. Various methods are available to remove and isolate these heavy metals from water and wastewater such as ion-exchange, chemical precipitation, membrane filtration, adsorption, and electrochemical treatment technologies [9]. This review paper provides an outline of a number of the literatures on utilization of low price adsorbents for zinc removal from contaminated water. The readers are requested to seek advice from the original articles for additional data on experimental conditions
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