Abstract
In this work, we present the possibility to reduce the amount of fluoride ions in silica gel waste by using different techniques or to immobilize these ions by creating products of commercial value. The leaching of fluoride ions from silica gel waste to the liquid medium was done under static and dynamic conditions. It was determined that the removal of fluoride ions from this compound depends on various factors, such as dissociation, solubility, the w/s ratio, reaction temperature, leaching conditions, the adsorption properties of silica gel waste, and others. The obtained results showed that, by applying different techniques, the quantity of fluoride ions can be reduced by 60%, while obtained water was neutralized by calcium hydroxide. Additionally, it was determined that silica gel waste is a promising raw material for the hydrothermal synthesis of a stable compound containing fluoride ions–cuspidine.
Highlights
The disposal of industrial by-products is becoming an increasing concern for many industries due to the large amounts of wastes generated and increasing costs of operating landfills in combination with the scarcity of landfill sites [1,2,3,4,5,6,7,8]
The structure of the precipitated silica gel waste depends on many variables: the duration of the reaction, the temperature, the way in which reagents are dosed, the structure of Al(OH)3 used in the process, and the purity of the applied fluorosilicic acid [13]
The chemical analysis data showed that dried (50 ◦C, 48 h) silica gel waste (SGW) consists of 79.0% SiO2 and 10.0% F−
Summary
The disposal of industrial by-products is becoming an increasing concern for many industries due to the large amounts of wastes generated and increasing costs of operating landfills in combination with the scarcity of landfill sites [1,2,3,4,5,6,7,8]. Large amounts of silica gel waste contaminated with fluoride ions are generated in the industrial production of aluminum fluoride [13,14]. Because of the high cost of silica gel waste processing, it is preferably discharged in landfill sites [13,16,17,18]. Long-term storage and maintenance of silica gel waste are currently facing many environmental concerns, which are associated with the dumps and disposal sites of this by-product due to the leaching of fluoride into the surface and underground water [13,16]
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