A review on the modification techniques to enhance the heavy metals sorption capacity of kaolin clay from south east Vietnam

Abstract

For decades, adsorption has been proved to be the best process of contaminated water treatment because of its simplicity and lower costs as compared to other traditional technologies. Clay minerals are promising natural adsorbents for removing many pollutants such as heavy metals, organic and biological pollutants. Kaolin, which composed of kaolinite and has layered structure. This clay is dominant in South East Vietnam, which is why research about its usage in heavy metal adsorption is important. But due to the lower cation exchange capacity and surface area so it is not widely used. However, natural kaolin can be easily modified to improve their surface properties (e.g., surface area, charge) and consequently increase the adsorption capacity and a wide range of other applicability. In order to improve kaolin's sorption capacity, many modification methods were tested such as thermal modification, acid activation, and/or novel clay composites. Kaolin, both in its natural and modified forms, effectively removes various heavy metals from aqueous solution, as extensively discussed in this review. This detailed review compiles thorough literature of current research over the last twenty years (2000–2020) and highlights the key findings of modifications of kaolin that were done to enhance its sorbent capacity. The effect of the experimental conditions on the adsorption capacity is also appraised. It will also evaluate the adsorption mechanisms, structures, and adsorptive characteristics of natural and modified clay. Furthermore, the adsorption efficiencies and identify the feasibility to widespread uptake of the technology in South East Vietnam are included. It revealed that agricultural waste and nano zero-valent iron modified kaolin is applicable for kaolin from South East Vietnam.