Recent advances in kaolin for adsorption of water pollutants
Significance Nowadays,the increasing concentration of pollutants in industrial wastewater has caused serious pollution of water resources,which has affected the daily life and health of human beings.The traditional methods of treating water pollutants are mainly divided into biological treatment,physical treatment and chemical treatment.Among them,the adsorption is the most widely used in the physical treatment methods,but the traditional adsorbents are limited by their expensive and difficulty in sepa-rating from water.Hence,much attention has been paid to the preparation of a new type of adsorbent that is economical and easy for solid-liquid separation.Kaolin is a resourceful,cheap and easily available,non-toxic non-metallic mineral clay resource.The chemical formula of its crystals is Al2 O3·2SiO2·2H2 O.The application of kaolin has limited in industrial fields such as paper,paint,rubber,ceramics,etc.,while the fields of catalytic and pollutant treatment are still lack of application.In recent years,these materials have attracted the attention of researchers due to its advantages of abundant,cheap and easy availability.Progress The development on the adsorption of heavy metal pollutants,organic pollutants and other pollutants such as F-in water by raw kaolin,organo-inorganic modified kaolin and composite modified kaolin is summarized.kaolin itself is reported to have certain adsorption and ion-exchange capacity.However,the adsorption efficiency of raw kaolin is unsatisfactory.Therefore,researchers have tried various possible ways to modify kaolin,such as inorganic acid and alkali modification of the raw or calcined kaolin,organic modification using silane coupling agent,DMSO,etc.,and composite modification with organic substances such as chitosan or alginate,and inorganic substances including titanium oxide and magnetic iron.The results of adsorption perform-ance of water pollutants show that different modification methods can improve the adsorption performance of kaolin on water pollu-tants.For example,calcination and acid or base treatment can improve the specific surface area of kaolin and enhance its adsorp-tion performance.The composite modification of kaolin to diversify the adsorption sites and effectively improve the adsorption performance is a much-studied topic.Researchers have also discussed the adsorption mechanism to different degrees,and most of the adsorption isotherms are fitted with the Langmuir model,and most of the adsorption kinetics is consistent with the pseudo-second-order model.Conclusions and Prospects The research on the adsorption of kaolin for removal of water pollutants has been gradually developed,with various modification methods.However,there remains a challenge to efficiently improve the adsorption performance of kaolin.More research should be focused on how to improve the adsorption properties of kaolin while exploring low energy consumption,low cost,simple process,environmentally friendly modification methods that effectively improves the value of kaolin resources.
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