S. Ndiaye, A. Toure, F. Sambe
Jun 20, 2021
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Influential Citations
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Journal
Waste and Biomass Valorization
Abstract
The production of phosphoric acid for use in fertilizer generates toxic fluorosilicic acid as by-product, which can have, when disposed in ocean, negative effects on the maritime ecosystem. With the objective of developing a process for the treatment and valorization of this industrial waste, we study a route starting with a reaction between fluorosilicic acid and sodium chloride that produces a hydrochloric acid solution and sodium fluorosilicate powder. In the present work, we focused on the conversion step of sodium fluorosilicate, consisting of a caustification reaction in an aqueous solvent, with the purpose of obtaining valuable products. We identified a reaction scheme based on a preliminary thermodynamic study using the PHREEQC geochemical software. Experimental tests were then carried out in a 2 L stirred batch reactor, with various characterization techniques of the products (ICP-OES, XRD, TGA) allowing to establish mass balances. We propose two new steps in the conversion process, consisting of the aqueous reaction of CaO with Na2SiF6 at 50 °C, with an intermediate filtration for a molar ratio (CaO/Na2SiF6) of 2.77. This process generates two solid products: (i) pure CaF2, which can be used as an additive in various pyrometallurgical processes and (ii) a mixture of calcium silicate hydrates with low content of CaF2, which constitutes a promising resource for construction and building materials.