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Updated: Sep 30, 2026

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent
Published on: February 21, 2017
Recycling oyster shell waste as a bio-derived pore-promoting additive for porous phosphate-based geopolymers produced
Steve Keyrane Kuida Tchikapa1, Priscilla S Brunetto2, Antoine Scalabre2
1Applied Physical and Analytical Chemistry Laboratory, Department of Inorganic Chemistry, University of Yaoundé I Yaoundé Cameroon beplacide85@gmail.com keyranekuida70@gmail.com.
Abstract:
Porous phosphate-based geopolymers were synthesized from volcanic slag using calcined oyster shell waste (COS) as a bio-derived calcium source and pore-development promoting additive. Volcanic slag was partially substituted with 0, 5, 10, and 15 wt% COS and activated with phosphoric acid solutions of 6 and 10 mol L-1. The influence of COS incorporation on phase evolution, microstructure development, and engineering performance was investigated using XRD, FTIR, SEM/EDS, TGA/SDTA, and physicomechanical analyses. The results revealed that phosphoric acid concentration and calcium availability jointly controlled precursor dissolution and reaction-product formation. Calcium released from COS promoted the precipitation of calcium phosphate phases, predominantly monetite (CaHPO4), while phosphoric acid activation favored the formation of a continuous aluminosilicophosphate matrix. The balance between these competing processes governed pore development and matrix continuity. Among the investigated formulations, the 5 wt% COS composition generated the most favorable balance between homogeneous pore development and compressive strength (21.74 MPa compared with 22.85 MPa for the reference formulation). Higher COS contents increased microstructural heterogeneity, efflorescence, and strength loss. This study provides mechanistic insights into pore formation in phosphate-based geopolymers and demonstrates a promising waste-valorization route for converting oyster shell waste and volcanic slag into functional porous materials.
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