Selective Adsorption and Removal of Heavy Metals From Seawater By Nanosorbents

Heavy metal pollution in seawater is an increasing concern due to the rapid growth in seawaters use from industrial oil extraction to district cooling installation and in production of potable waters to supplement the diminishing supply of fresh waters. Heavy metal can persist and accumulate with long-term and wide-ranging impact on marine ecosystem. It is therefore important to develop technology that can effectively remedy metal pollution in seawater. The sorption process remains the most economical means of removing heavy metals, but the high salt and organic content of seawater pose important challenges. This work investigates the design and preparation of functionalized nanosorbents for selective adsorption and removal of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, As(V), Sb(III), Cr(VI) from seawater. 

Mono-/di- /tri- amino-organoalkoxysilanes were grafted on the walls of MCM-41 to capturing heavy metal cations (e.g. Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺ ) and Fe³⁺ sorption to the amino groups to create adsorbents for removing heavy metal anions (e.g. As(V), Sb(III), Cr(VI)). The experimental results showed NH₂-MCM-41 can selectively remove more than 99% copper with a Kd of 10⁶ from seawater at pH 8, while the NNN-MCM-41 has good affinity for adsorption of cadmium from seawater. The Fe-NNN-MCM-41 nanosorbent on the other hand removes Cr(VI) from seawater (pH8) with a removal percentage of >99% and Kd of 10⁶. Batch and fixed-bed column adsorption studies were carried out to obtain the adsorption kinetics and isotherm for potential practical application.