https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33682 2+ and Cd²⁺ on defluoridation by calcite because Spent Pot Lining (SPL, a byproduct generated during the aluminum production) leachate is a complex chemical cocktail. To better understand defluoridation processes and replicate the situation in the field, column tests were conducted. Results indicate that presence of neither Ba²⁺ nor Cd²⁺ has significant impact on fluoride retention when compared with the blank (no metals) because the relative concentration values (F/F_o) as well as the transport parameters like retardation factor (R_c) and distribution coefficient (K_d) are almost the same. PHREEQC, a geochemical software, was then applied to simulate the column test processes (i.e., 1D reactive/transport processes) based on the mechanism of CaF₂ precipitation followed after calcium dissolution. As indicated in the batch reactor test, addition of Cd²⁺ may inhibit calcite dissolution; therefore, a new phase "CalciteSupp" (a phase representing the suppressed solubility of calcite) was defined. Modeling results exhibit good predictions of observed data, and the log_k solubility of the hypothetical "CalciteSupp" equilibrium phase implies the suppression of calcite dissolution in the metal samples. Moreover, saturation indices obtained by modeling indicate the precipitation of CdCO₃ and BaCO₃, revealing that addition of metals may influence fluoride removal at some point during the process, but has no big impact on overall defluoridation. The initial development of the PHREEQC geochemical model presented shows potential in being able to be used as a predictive tool for the design of fluoride remediation strategies, such as permeable reactive barriers, and transport parameters obtained on the basis of the column tests, and CXTFIT (a computer program for evaluating and estimating transport parameters) modeling can be applied in practical design.]]> Wed 05 Dec 2018 12:10:50 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33681 −1. Fluoride removal half-life (t_0.5) values were found to increase in the order Ba ≈ stonedust (a 99% pure natural calcite) < Cd < Co < Mn. A barrier width of 0.97 ± 0.02 m was found to be required for the fluoride/calcite (stonedust) only system when using no factor of safety, whilst in the presence of Mn and Co, the width increased to 2.76 ± 0.28 and 19.83 ± 0.37 m respectively. In comparison, the PSO model predicted a required barrier thickness of ∼46.0, 62.6 & 50.3 m respectively for the fluoride/calcite, Mn and Co systems under the same conditions.]]> Wed 04 Dec 2019 12:54:35 AEDT ]]>