(713g) Biopolymer Enhanced Fly Ash-Based Geopolymer for Water Purification

Geopolymers (an inorganic polymer), and chitosan biopolymer materials have been widely studied and shown to exhibit significant individual strengths (and some weaknesses) in removing a variety of heavy metals from aqueous solution. While the former is made with the abundant precursor (e.g., fly ash), the latter is more costly and is synthesized from less abundant chitin. In this research effort an innovative strategy involving a focused experimental approach coupled with thermodynamic modeling (TM) is applied to formulate geopolymer-chitosan composite to leverage on synergistic interaction between the biopolymer and the hydrate phase assemblage of the geopolymers, (e.g., amorphous polymeric hydrogel, crystalline zeolites, and (Ca/Mg)-Al-layered double hydroxides) to provide high performance (in terms of heavy metal (HM)-sorption capacity/$) that is many times better than commercial adsorbent (e.g., activated carbon).

To this end, hybrid geopolymers of various formulations – guided by thermodynamic modeling – are prepared using different fly ash compositions (e.g., low Ca – to – High Ca fly ash), mix designs (i.e., activator solution of different chemistries, and liquid-to-solid ratio) and curing conditions (e.g., temperature and pressure), wherein fly ash is the main precursor with minor dosage of the more costly chitosan (0.05 –to-2 wt%). The performance of the prepared hybrid materials are investigated by batch sorption experiments to determine their performance in removing aqueous heavy metals (particularly: Pb²⁺, Zn²⁺, Cd²⁺, Cu²⁺ As³⁺, Se^2-, and Hg²⁺). Additionally, the mechanical properties (i.e., strength, hardness, and abrasion) and chemical durability are tested. The expected outcome will provide insights on optimum geopolymer microstructure and chitosan dosage for a synergistic combination of the excellent individual properties of both materials leading to a hybrid material with exceptional performance for aqueous heavy metal removal, high durability, and yet low-cost.

Keywords: Geopolymer; Biopolymer; Heavy metal removal