A novel conversion process for waste slag: synthesis of calcium silicate hydrate from blast furnace slag and its application as a versatile adsorbent for water purification

Abstract

Blast furnace slag (BFS), a high volume byproduct resulting from the iron manufacturing industry, was used as a low-cost and abundant precursor for preparing a high-surface-area calcium silicate hydrate. The synthesis of slag-made calcium silicate hydrate (slagCS) was achieved via a facile two-step dissolution–coprecipitation procedure using HCl and NaOH, respectively. The use of concentrated protonic acid facilitated an easy dissolution of BFS, and the subsequent addition of aqueous NaOH solution at 100 °C yielded a hydrate product with over 85% atom economy (10.9 g from 10.0 g of BFS). By the combination of XRD, FT-IR, ²⁹Si MAS NMR, FE-SEM, nitrogen physisorption and chemical analysis, the product synthesized under optimum conditions was identified to be a calcium silicate hydrate with a stoichiometry of Ca : Si = 1 : 1 and with a mean surface area of 219 m² g⁻¹ incorporating the slag-derived metals (Al, Mg, Fe, Ti and Mn) in its structure. The thus synthesized slagCS showed good adsorption properties for removal of Cu²⁺, phosphate ions and model protein (ovalbumin) diluted in water, making this material a promising candidate for efficient bulk wastewater treatment.