MODIFICATION, CHARACTERIZATION, AND APPLICATION OF NANOCLAY FOR WATER TREATMENT

Abstract

The development of low-cost, environmentally friendly, and efficient treatment processes has been the subject of global importance at the rise of the century, specifically from industries, governments, and researchers alike. This was mandated to address the issues of water scarcity and water security, which coexist in many parts of the world and towards developing sustainable solutions. In regions where seawater desalination prevails for the generation of drinking water and other water applications, the use of alternative water sources is essential in maintaining water sustainable approaches. While groundwater is generally one of the preferred water sources in arid regions due to its convenient availability, its over-extraction and anthropogenic contamination make it limited for use. The reuse of treated wastewater in industrial applications is deemed to be a reliable water source. However, high residual nutrients such as phosphate could make it unsuitable for its disposal in natural waters or reuse in certain industrial applications such as in cooling towers._x000D_ Resorting to membrane processes could be a good step towards developing a more sustainable environment; however, membranes are prone to scaling and fouling due to total dissolved solids (TDS) (e.g. calcium, magnesium, nitrates, and phosphates), hydrocarbons, and microorganisms available in the source water and require a pre-treatment step. Adsorption is considered to be one of the most attractive options for water pre-treatment due to its high efficiency, simplicity, and cost effectiveness. _x000D_ This dissertation presents the use of two different types of modified nanoclay minerals for their application in a pre-treatment, for the removal of arsenic and phosphate before a membrane process for water treatment, or a post-treatment stage (effluent polishing). Clay minerals and their modified counterparts lie within a group of adsorbents used for the adsorption of many chemical contaminants from an aqueous solution. Amongst this group, montmorillonite (MMT) clay, distinguished by its 2:1 layered structure, has been of wide interest amongst researchers. Halloysite nanotubular (HNT) clay is a naturally occurring mineral with a nanotubular structure. Its chemical structure and properties denote it as a novel alternative material for adsorption. _x000D_ The modification of MMT and HNT with environmentally benign modifiers such as iron (hydr)oxide provides a ‘green’ class of adsorbents that are selective towards the removal of the contaminants presented in this work. This study also involves the development and characterization of low-cost adsorbents through the modification of MMT and HNT with iron (hydr)oxides using a minimum number of precursors and their application as filters for water treatment for arsenic and phosphate removal in contaminated waters. _x000D_ Our results demonstrated the enhancement of the adsorption capacity of MMT towards arsenite As (III) removal by more than five times after hydroxyiron modification. More than 55% of As (III) was removed within the first 30 s of the adsorption process at an initial As (III) concentration of 1 ppm. The modification of MMT and HNT clay with iron oxide nanoparticles using an easy to scale-up procedure provided innovative nanosorbents for the adsorption of phosphate from water. Iron oxide modified MMT removed more than 40% of phosphate from water, while iron oxide modified HNT removed more than 60% of phosphate from water at a pH of 7 and an initial phosphate amount of 10 ppm. More than 80% of phosphate was removed at a pH of 4 using 1Fe-HNT. The presence of coexisting anions in water such as sulfate, nitrate, and chloride were shown to enhance the removal of phosphate from water at an initial phosphate amount of 10 ppm. Batch adsorption experiments testing the raw and modified adsorbents were conducted using real wastewater with an initial phosphate concentration of 1.34 mg/L and more than 90% removal of phosphate was observed using the modified adsorbents. _x000D_ The application of the developed nanosorbents could be used for the removal of contaminants such as arsenic from arsenic contaminated groundwater or for phosphate removal in treated wastewater such as treated sewage effluent for ‘effluent polishing’.

Date of Award	2018
Original language	American English
Awarding Institution	HBKU College of Science and Engineering