- Title
- Effects of pCO₂ on the removal of fluoride from wastewater by calcite
- Creator
- Sleap, Scott B.; Turner, Brett D.; Krabbenhøft, Kristian; Sloan, Scott W.
- Relation
- Australian Research Council.LP100200488
- Relation
- Journal of Environmental Engineering Vol. 139, Issue 8, p. 1053-1061
- Publisher Link
- http://dx.doi.org/10.1061/(ASCE)EE.1943-7870.0000710
- Publisher
- American Society of Civil Engineers
- Resource Type
- journal article
- Date
- 2013
- Description
- Free-drift batch reactor experiments using calcite (limestone, CaCO₃) were used to study fluoride removal through precipitation as fluorite (CaF₂) from solutions with concentrations reflective of an industrially contaminated site. The influence of CO₂ partial pressure (pCO₂), stirring rate, and fluoride concentration were investigated in this paper. Equilibrium modeling shows that in wastewaters with high fluoride concentrations (~2,000 mg/L), the flux of CO₂(g) to CO₂(aq) could not keep up with the consumption of CO₂(aq), resulting in an initial disequilibrium with experimental pH reaching equilibrium quickly, while fluoride removal lagged. Increasing stirring rate significantly decreased the extent of disequilibrium and the time at which the CaCO₃ -fluoride-CO₂ system attained equilibrium due to the increased rate of transport of dissolved CO₂ to the CaCO₃ surface, and simultaneously the rate of transport of the dissolved CaCO₃ to the bulk solution. Optimal fluoride removal occurs at pCO₂ ~10-0.52 [30% (mol% CO₂)] with 96% of the initial 2,000 mg/L fluoride load removed in less than 80 min with a stirring rate of 300 revolutions per minute. Increasing pCO₂ to ~100 (100% CO₂) resulted in very little gain, less than 2%, in fluoride removal, or in the time required to reach equilibrium and therefore significant remediation cost savings can be obtained by using pCO₂ 30% when compared to 100%.
- Subject
- industrial waste; remediation; wastewater management; groundwater; limestone; carbon dioxide; inorganic compounds
- Identifier
- http://hdl.handle.net/1959.13/1060906
- Identifier
- uon:16839
- Identifier
- ISSN:0733-9372
- Language
- eng
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