The Prospective Approach for the Reduction of Fluoride Ions Mobility in Industrial Waste by Creating Products of Commercial Value

Abstract

In this work, we present the possibility to reduce the amount of fluoride ions in silica gelwaste by using different techniques or to immobilize these ions by creating products ofcommercial value. The leaching of fluoride ions from silica gel waste to the liquid medium wasdone under static and dynamic conditions. It was determined that the removal of fluoride ionsfrom 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 ionscan 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 thehydrothermal synthesis of a stable compound containing fluoride ions – cuspidine.

Conversion of silica by-product into zeolites by thermo-sonochemical treatment

“…Silica by-product is material based on amorphous SiO 2 polluted with fluoride compounds. This by-product was obtained from fertilizer plant (Lithuania) and it accumulated about 15,000 tons yearly [14] . Silica by-product is a silica hexaflouride acid neutralization product.…”

“…These fluoride compounds retarded the setting process and decreased the mechanical properties of hardened cement pastes or concretes as well. It was suggested thermal treatment [13] or chemical purification method of silica by-product [12] , [14] . All these suggestions are related with the elimination or neutralization of problematic fluoride compounds.…”

A Novel and Efficient Metal Oxide Fluoride Absorbent for Drinking Water Safety and Sustainable Development

“…MgCl2•6H2O, FeSO4•7H2O and Ce(SO4)2•4H2O were dissolved for the mixed solution with a molar concentration ratio of Mg:Fe:Ce of 4 To choose the best synthetic method for the adsorbent, two synthesis methods (i.e., the co-precipitation method and hydrothermal synthesis method) were compared. The detailed co-precipitation method was (1) preparing the required experimental solution, (2) adjusting pH with 6 mol•L −1 NaOH to 8.5 and keeping this pH more than 30 min, (3) keeping still for more than 24 h, (4) washing the acquired precipitate and centrifuging all the mixed solution-including precipitate and washing water, (5) drying the precipitate under 65 • C for 24 h, and (6) calcining in the muffle furnace at 600 • C. The detailed hydrothermal synthesis method was (1) preparing the required experimental solution, (2) adding the solution and 6mol•L −1 NaOH to the autoclave and fastening the gap, (3) heating for 6 h under 90 • C, (4) sampling after cooling and exhausting, (5) washing the acquired precipitate and centrifuging all the mixed solution-including precipitate and washing water, (6) washing and drying the precipitate under 65 • C, and (7) calcining in the muffle furnace at 600 • C.…”

“…Sustainability 2021, 13, 883 2 of 18 Numerous efforts have been devoted to effective F − removal technology development [6][7][8], such as precipitation [9], electrocagulation [10], membranes [11], ion exchange [12][13][14], and adsorption [15][16][17][18]. For example, Shen et al (2003) proposed a treatment measure through the combined electrocoagulation and electroflotation process to remove fluoride ions and found that the anions had a negative effect on fluoride removal efficiency [10].…”

“…Kumar et al (2020) advanced both activated alumina (AA) and grinded activated alumina (GAA) for adsorption potential by batch experiments for different contact time, pH, fluoride concentration, and adsorbent dose for fluoride adsorption [26]. From the above analysis, activated alumina is a popular treatment technology for F − removal due to its availability and low cost, and there are some limitation on frequent regeneration with aluminum sulfate under a lower adsorption capacity at a neutral pH (5)(6) [27]. Furthermore, residual alumina in treated water may cause adverse health effects due to its characteristics and 5-10% loss of adsorbency on regeneration [28].…”