Limestone can be an option for sulfate sorption, particularly from neutral mine drainages because calcium ions on the solid surface can bind sulfate ions. This work investigated sulfate removal from mine waters through sorption on limestone. Continuous stirred-tank experiments reduced the sulfate concentration from 588.0mg/L to 87.0mg/L at a 210-min residence time. Batch equilibrium tests showed that sulfate loading on limestone can be described by the Langmuir isotherm, with a maximum loading of 23.7mg/g. Fixed-bed experiments were utilized to produce breakthrough curves at different bed depths. The Bed Depth Service Time (BDST) model was applied, and it indicated sulfate loadings of up to 20.0gSO(4)(2-)/L-bed as the flow rate increased from 1 to 10mL/min. Thomas, Yoon-Nelson and dose-response models, predicted a maximum particle loading of 19mg/g. Infrared spectrometry indicated the presence of sulfate ions on the limestone surface. Sulfate sorption on limestone seems to be an alternative to treating mine waters with sulfate concentrations below the 1200-2000mg/L range, where lime precipitation is not effective. In addition, this approach does not require alkaline pH values, as in the ettringite process.

Manganese removal from mining-affected waters is an important challenge for the mining industry. Addressed herein is this issue in both batch and continuous conditions. Batch experiments were carried out with synthetic solutions, at 23+/-2 degrees C, initial pH 5.5 and 8.3 g limestone/L. Similarly, continuous tests were performed with a 16.5 mg/L Mn(2+) mine water, at 23 degrees C, initial pH 8.0 and 20.8 g limestone/L. Calcite limestone gave the best results and its fine grinding proved to the most effective parameter for manganese removal. In either synthetic solutions or industrial effluents, the final manganese concentration was below 1 mg/L. A change in limestone surface zeta potential is observed after manganese removal and manganese carbonate formation was suggested by IR spectroscopy. The conclusion is that limestone can remove manganese from industrial effluents for values that comply with environmental regulations.

a b s t r a c tThe mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 • C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm −1 attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the 4 spectral region between 700 and 550 cm −1 offers evidence for the reduction in symmetry of the sulphate anion from T d to C 2v or even lower symmetry. The Raman band at 3629 cm −1 is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm −1 to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.

(Iron ore direct flotation with sodium oleate) ResumoO objetivo desse trabalho foi estudar a possibilidade de concentração de minério de ferro por flotação direta, usando oleato de sódio como coletor dos minerais de ferro e o metassilicato de sódio como depressor da ganga silicosa. Após a caracterização das amostras minerais e do minério, foram feitos estudos fundamentais, que englobaram a determinação do potencial zeta dos minerais hematita e quartzo, cujos valores de PIE ocorreram em pH 7,5 e 1,8, respectivamente. Os ensaios de microflotação, em tubo de Hallimond modificado, determinaram as condições de maior flotabilidade da hematita, 50 mg/L de oleato de sódio em pH 7, e do quartzo, 70 mg/L de oleato de sódio em pH 9. Os ensaios de microflotação, ainda mostraram que o metassilicato de sódio foi mais efetivo na depressão da hematita que na depressão do quartzo. Os ensaios de flotação em bancada confirmaram esse comportamento, ou seja, o metassilicato de sódio não propicia separação seletiva entre a hematita e o quartzo durante a flotação. O melhor concentrado fornecido pela flotação direta da amostra de minério de ferro, cujos teores de Fe e SiO 2 eram, respectivamente, de 35,34 e 48,02%, foi obtido usando-se dosagens de 600 g/t de metassilicato de sódio e 1200 g/t de oleato de sódio: recuperação metalúrgica de Fe de 88%, teor de Fe de 58,1% e teor de SiO 2 de 14,4%. Palavras -chave:Flotação direta, minério de ferro, oleato de sódio, metassilicato de sódio. Abstract

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The mineral kovdorskite Mg2PO4(OH)·3H2O was studied by electron microscopy, thermal analysis and vibrational spectroscopy. A comparison of the vibrational spectroscopy of kovdorskite is made with other magnesium bearing phosphate minerals and compounds. Electron probe analysis proves the mineral is very pure. The Raman spectrum is characterized by a band at 965 cm(-1) attributed to the PO4(3-) ν1 symmetric stretching mode. Raman bands at 1057 and 1089 cm(-1) are attributed to the PO4(3-) ν3 antisymmetric stretching modes. Raman bands at 412, 454 and 485 cm(-1) are assigned to the PO4(3-) ν2 bending modes. Raman bands at 536, 546 and 574 cm(-1) are assigned to the PO4(3-) ν4 bending modes. The Raman spectrum in the OH stretching region is dominated by a very sharp intense band at 3681 cm(-1) assigned to the stretching vibration of OH units. Infrared bands observed at 2762, 2977, 3204, 3275 and 3394 cm(-1) are attributed to water stretching bands. Vibrational spectroscopy shows that no carbonate bands are observed in the spectra; thus confirming the formula of the mineral as Mg2PO4(OH)·3H2O.

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