Exploration of a Two-Step Aqueous Process for the Valorization of Sodium Fluorosilicate (Na2SiF6), an Intermediate Product of the Fluorosilicic Acid Conversion

Ndiaye, Samba; Touré, Awa Oumar; Sambe, Falilou Mbacké; Diop, Codou Mar; Prat, Laurent E.; Cassayre, Laurent

doi:10.1007/s12649-021-01496-w

Cited by 9 publications

(4 citation statements)

References 34 publications

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“…Second, the CSH material was synthesized following an aqueous route designed to transform H 2 SiF 6 into secondary raw materials. As described in our previous work, the synthesis results from a three-step aqueous process consisting in (1) an aqueous reaction between H 2 SiF 6 and NaCl to form solid Na 2 SiF 6 and a concentrated HCl solution, (2) an aqueous reaction between Na 2 SiF 6 and CaO to form solid CaF 2 and a (Si, Na)-rich solution, (3) a further addition of CaO in the filtrate, leading to the precipitation of CSH and secondary phases, which are recovered by filtration from a Na-rich aqueous solution.…”

Section: Materials and Methodsmentioning

confidence: 99%

“…As discussed in our previous work, the presence of CaF 2 is specific of our process and its amount can be tuned by the amount of CaO added during the first reaction step. The presence of CaCO 3 is attributed to the partial carbonation of the material during the drying step (nitrogen bubbling was implemented during the alkaline precipitation in order to minimize CO 2 uptake).…”

Section: Materials and Methodsmentioning

confidence: 99%

“…In the worldwide phosphate fertilizer production, more than 2 million tons of hexafluorosilic acid are generated annually as a result of the reaction of phosphate ore and sulfuric acid. , The valorization of this acid remains a global environmental challenge and generates research efforts. ,− For instance, superphosphate plants such as Industries Chimiques du Senegal discharge nearly 276000 m 3 /year of H 2 SiF 6 into the sea for a production of 600000 tons/year of phosphoric acid. In our previous work, we proposed a three-step aqueous process to treat waste solutions containing 250 to 300 g/L of H 2 SiF 6 issued from phosphoric acid production. It consists of a first aqueous reaction between H 2 SiF 6 and NaCl to form solid sodium fluorosilicate Na 2 SiF 6 and a concentrated HCl solution, followed by a reaction between sodium fluorosilicate and lime, allowing to successively generate two solid products: pure CaF 2 , which can be used as an additive in various pyrometallurgical processes and calcium silicate hydrates (CSH) containing about 10 wt % CaF 2 .…”

Section: Introductionmentioning

confidence: 99%

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Carbonation of Calcium Silicate Hydrates as Secondary Raw Material from the Recovery of Hexafluorosilicic Acid

Ndiaye

Pisch

Touré³

et al. 2022

ACS Sustainable Chem. Eng.

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This work focuses on the carbonation reaction of calcium silicate hydrates (CaO)(SiO 2 )(H 2 O) (CSH) powders synthesized by an aqueous process using fluorosilicic acid waste and lime as main reactants. We investigated whether these CSH could constitute a secondary raw material to produce building materials that harden at low temperature by reaction with CO 2 , according to a process that is commonly based on the use of minerals such as natural wollastonite (CaSiO 3 ). CSH and wollastonite powders were placed in a gas stream consisting either of pure CO 2 or of a 15 vol % CO 2 −85 vol % air mixture, saturated with water, at atmospheric pressure and 40 °C. Based on thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy of the products, we proved the occurrence of the carbonation reaction and we calculated the carbonation degree α for various reaction times. The structural water contained in the CSH played a beneficial role in the carbonation reaction since their carbonation degree is much higher than that of wollastonite: for a reaction time of 120 min at 40 °C, α = 75% for CSH against 12% for CaSiO 3 . Furthermore, carbonation promotes the formation of calcite with only 15 vol % CO 2 , allowing the direct use of cement plant fumes.

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Section: Materials and Methodsmentioning

confidence: 99%

Section: Materials and Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Carbonation of Calcium Silicate Hydrates as Secondary Raw Material from the Recovery of Hexafluorosilicic Acid

Ndiaye

Pisch

Touré³

et al. 2022

ACS Sustainable Chem. Eng.

Self Cite

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“…The carbon-emission coefficient of each material was obtained from the China Products Carbon Footprint Factors Database. Some materials, such as SH, CGN, PS, and SSF, are estimated by analyzing the possible carbon emissions generated through their production processes; therefore, the results may be inaccurate [21,[55][56][57][58].…”

Section: Objective Functionsmentioning

confidence: 99%

Mixture optimization for mechanical, environmental, and economic objectives in grouting slurry for repairing earthen sites

Cui,

Shao,

et al. 2024

Herit Sci

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Anchor and fissure grouting are used to repair earthen sites. However, the common method to obtain the compressive strength of grouting slurry would cause material, labor, and time losses. In addition the material properties, environmental and economic benefits have gained increasing attention. This study proposes a design framework for multi-objective proportioning optimization based on machine learning and metaheuristics. The results indicated that the eXtreme Gradient Boosting (XGBoost) model, whose hyper-parameters were optimized by a genetic algorithm, can accurately predicted the compressive strength of the slurries. The impact of the variables on development of compressive strength can explain the internal reaction mechanisms. The analytical framework based on meta-heuristic and technique for order of preference by similarity to an ideal solution (TOPSIS) provided Pareto-optimal solutions in design scenario of each sub-dataset. The framework proposed in this study can efficiently achieve mechanical, environmental, and economic design objectives of anchor grouting and fissure grouting slurries for repairing earthen sites.

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Improvement of the characterization uncertainty of a matrix-certified reference material for accurate measurement of H2SiF6 mass fraction in industrial fluorosilicic acid by using a direct measurement procedure

et al. 2023

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Exploration of a Two-Step Aqueous Process for the Valorization of Sodium Fluorosilicate (Na2SiF6), an Intermediate Product of the Fluorosilicic Acid Conversion

Cited by 9 publications

References 34 publications

Carbonation of Calcium Silicate Hydrates as Secondary Raw Material from the Recovery of Hexafluorosilicic Acid

Carbonation of Calcium Silicate Hydrates as Secondary Raw Material from the Recovery of Hexafluorosilicic Acid

Mixture optimization for mechanical, environmental, and economic objectives in grouting slurry for repairing earthen sites

Improvement of the characterization uncertainty of a matrix-certified reference material for accurate measurement of H2SiF6 mass fraction in industrial fluorosilicic acid by using a direct measurement procedure

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