Preparation and characterization of porous metakaolin-based inorganic polymer spheres as an adsorbent

This paper describes a simple and effective process for fabricating porous metakaolin-based inorganic polymer spheres. The process for making porous geopolymer spheres (PGS) by a suspension and solidification method was experimentally established, and the following conditions yielded the optimal compositions: n(SiO2)/n(Na2O) = 1.6 in a sodium silicate solution, n(Na2O)/n(Al2O3) = 1, n(H2O)/n(Na2O) = 16, sodium dodecyl sulfate (K-12) foaming agent = 1.5 mass%. This procedure was based on the rapid solidification mechanism of a geopolymer paste in a high-temperature suspension. Pore structure analysis of the geopolymer spheres revealed that the pore size distribution centered mainly at 15 nm, which indicated the presence of a large BET surface area (53.95 m(2)/g) of a mostly mesoporous nature. The bulk density of the spheres was 0.79 g/cm(3), and their total porosity was 60.30%; these results indicated the availability of numerous active sites for binding with Cu2+, Pb2+, Ca2+ and other ions. The results showed that porous geopolymer spheres are a low-cost, convenient, and environment-friendly adsorbent for removing metal ions. (C) 2015 Elsevier Ltd. All rights reserved.