查看更多>>摘要：The antibacterial chlorhexidine/vermiculite (CA/Ver) was successfully prepared through the intercalation process and the stability of CA on the vermiculite matrix and was investigated by stirring in aqueous solutions under the influence of different pH and temperature. The content of CA was determined by total organic carbon (TOC) analysis before and after stability tests. The structure of all samples was characterized by X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The antibacterial activity of prepared CA/Ver samples was evaluated by finding a minimum inhibitory concentration (MIC) against Entero coccus faecalis, Staphylococcus aureus, Escherichia coil and Psetidomonas aeruginosa. The content of chlorhexidine ranged from 209 to 231.6 mg of CA in 1 g of the whole sample after the intercalation process. After stability study, only a slight outflow of CA from the Ver matrix (<5%) was noted. The antibacterial test confirmed that the outflow of CA was negligible.
查看更多>>摘要：Rare earth elements (REE5) have an ever-increasing variety of applications in modern technology. In the present work, the possibility of extraction of rare earth elements cerium (Ce), lanthanum (La), neodymium (Nd) and thorium (Th) from a monazite concentrate containing 25% rare earth elements' oxide was investigated. In this regard, the acidic digestion and leaching step, and their effective parameters were studied in detail using design of experiment (DOE) which hadn't been investigated before. The optimum conditions for the performed experiments in acidic digestion step were: temperature of 225 degrees C, time of 3.5 h and sulfuric acid to concentrate weight ratio (L/S) of 2.5. Using these conditions, the recovery of 92.34%, 91.44%, 92.1% and 88.94% were obtained for cerium, lanthanum, neodymium and thorium, respectively. In leaching step, the optimum conditions were: temperature of 75 degrees C, time of 15 h and water to digested mass weight ratio of 7.5. Using these conditions, recovery of 88.47%, 89.45%, 87.35% and 82.19% were obtained for rare earth elements cerium, lanthanum, neodymium and thorium, respectively. In precipitation step, rare earths' oxalates were precipitated from the leach liquor using oxalic acid. Then, the precipitate was calcined in a furnace at 800 degrees C for 1 h and finally, a mixture of rare earth elements' oxides with a purity of about 84% was obtained. (C) 2016 Elsevier B.V. All rights reserved.
Pacheco, Anderson AlmeidaVergutz, Leonardusda Silva Souza-Filho, Luiz FranciscoAbdala, Dalton Belchior...
6页
查看更多>>摘要：Countries like Brazil, China and India are highly dependent on external reserves of soluble potassium (K) minerals for the production of K fertilizers. On the other hand, the natural occurrence of potassium-rich silicate minerals in these countries, has seldom been commercially exploited until recently. Technological strategies that can increase the reactivity of these minerals can turn them into a resource for K fertilizer production. This work aimed to investigate the changes in solubility of Verdete rock (VR) after calcination with a melting agent (MACaCl(2)center dot 2H(2)O) under varying temperatures of calcination and ratios (ww(-1)) of MA/VR. Measurements of extractable K in water (Kwater), X-ray diffraction (XRD) and X-ray Absorption Near Edge Structure (XANES) were performed to identify new mineral phases. The Kwater increased up to 184-fold when the VR was calcined in the presence of MA. Optimization of calcination of VR to temperature of 850 degrees C and a 1.7 ratio (ww(-1)) of MA/VR yielded Kwater values of up to 95% of total K. Potassium K-edge XANES analysis revealed changes in the molecular environment of K due to the calcination of VR at increasing temperatures. The K K-edge XANES fit to sylvite was supported by the detection of this mineral by XRD analysis at calcination temperatures ranging from 700 to 900 degrees C. In addition, K K-edge XANES analysis indicated the gradual formation of a new potassium-silicate mineral with increasing temperature, which the XANES analysis showed to be an amorphous-K2SiO3 (Amorphous-K2SiO3). The combination of Kwater and the residue of Linear Combination Fitting analysis (LCF) performed on the XANES data suggested the formation of an undefined K mineral phase additional to sylvite and Amorphous-K2SiO3. The calcination process was effective in producing highly soluble K mineral phases from a low solubility raw material. The end-products of the calcination procedure obtained in our work represent a promising alternative material for K fertilizer production, but further evaluation of the plant availability of the K in soils is needed. (C) 2016 Elsevier B.V. All rights reserved.
查看更多>>摘要：The similar flotability of scheelite, fluorite, and calcite resulted in the difficult separation by flotation. This work revealed the effect of water glass on the flotation of scheelite by FTIR and the wettability change of the usual cleavage plane, and proved that water glass inevitably influenced the flotation of tungsten minerals to a large extent in traditional fatty acid flotation process. A new collector, lead complexes of benzohydroxamic acid, was found to be selective for the separation of scheelite and calcium minerals with little water glass. Hence a novel flotation process was developed for the recovery of tungsten minerals in Shizhuyuan Mine in China. Normal temperature flotation of tungsten minerals was developed to instead of the classical "Petrov's process" for scheelitecalcite-fluorite type ores. Compared with the traditional process, the recovery was improved by almost 10% and the grade of scheelite concentrate was above 55%. The disappearance or decreasing of water glass contributed to improving the recovery of tungsten and the circulation of water and reagents. (C) 2016 Elsevier B.V. All rights reserved.
查看更多>>摘要：This study statistically investigated the turbidity removal of a dolomite/clay/borax-containing colloidal suspension that had a high degree of stability. During the destabilization experiments, the mixing intensity, the dosage of the coagulant and the flocculant was tested at fixed pH 9.40 due to the buffering property of dissolved borax. Then, the performance of the coagulation/flocculation process was evaluated with Response Surface Methodology (RSM) by using Box-Behnken Design. For the collected experimental data set, the different models were formed. However, the logarithmically transformed model (R-2: 99.75%; Adj-R-2: 99.30%) was selected as the most capable one for the physicochemical process. By using this enhanced statistical model, the optimum turbidity removal was acquired with the help of the design variables as follows: the mixing intensity of 265.138 s(-1), calcium chloride dosage of 305.585 mg/L and the flocculant dosage of 218.619 g/ton-solid. Based on this result, it can be concluded that the treatment of the tailings of borax concentrators can be feasible if the physical and the chemical parameters of the solid/liquid separation process are properly implemented all together. (C) 2016 Elsevier B.V. All rights reserved.
查看更多>>摘要：To understand the effect of aqueous impurities on chalcopyrite dissolution during acid metalliferous drainage and hydrometallurgical processes, batch dissolution experiments were carried out at 650 and 750 mV (SHE), pH 1 and 35-75 degrees C in the presence or absence of aqueous cationic additives. Activation energies (E-a) for chalcopyrite dissolution in the presence of additives at 750 mV, derived using a modified 'time to a given fraction' method, demonstrate that E-a varies with reaction extent. The overall trend of evolution from interface- to transport controlled mechanism was independent of additive type or addition. This suggests that it is not primarily variation in the enthalpy of dissolution that controls the significant changes in relative dissolution rates on addition of additives. Rather, the relative dissolution rates on addition of aqueous cations are found to relate to the M-O framework volume (M and O being the cationic additive and oxygen within H2O in the first sphere of hydration, respectively). There is good inverse linear correlation between this volume and the relative dissolution rate per unit ionic strength which varies as K+ > Al3+ > no additive > Mg2+ > Na+ > Ca2+. It is proposed that this effect is related to the relative strength of hydration of the additives with the commensurate entropic effect on solute hydration being advantageous for chalcopyrite dissolution on K+ and Al3+ addition and detrimental for the other additives. R4SiO4, the dominant aqueous species upon Si addition under the conditions examined, has low affinity for water, resulting in a detrimental entropic contribution to solute hydration and dissolution. The effect of Fe addition on relative dissolution rate is convoluted by the role of Fe3+ as the primary oxidant for chalcopyrite dissolution. On addition of aqueous Fe to dissolution at 750 mV, the effect is detrimental due to the detrimental effect on the entropy of hydration of the solute and the relative abundance of Fe3+. At 650 mV the effect of the greater presence of Fe3+ due to Fe addition dominates and the dissolution rate is enhanced. (C) 2016 Elsevier B.V. All rights reserved.
查看更多>>摘要：The use of laterite ore as a major nickel source is gradually increasing because of the depletion of sulphide ores. However, in contrast to high-grade nickel sulphide ore, low-grade nickel laterite ore cannot be as easily upgraded by current technologies due to its complicated mineral structure and nickel distribution. This study investigated the mineralogical characteristics, occurrence state and dissemination characteristics of nickel within Yunnan nickel laterite ore in China. Nickel laterite ore had a complex internal structure and mainly consisted of limonite (10 wt.%) and serpentine (87 wt.%). Sulphides were not a significant part of this laterite ore and were rarely observed. Furthermore, the nickel was mainly hosted in serpentine by substitution for Mg or by adsorption. Serpentine had a mean grade of approximately 0.77 wt.% Ni and represented approximately 81.49 wt.% of the total laterite resource. A portion of the laterite ore had a pore structure that was formed by destruction of the original protolith during and after its formation, with a specific surface area of 70.042 m(2)/g. The actual terhperature for the reduction of metal oxides within the ore was analysed by H-2-TPR (temperature-programmed reduction), which indicated that it was higher than the reduction temperature of the pure metal oxides. Finally, based on the above analyses, a non-melting reduction treatment process was proposed for efficient and reasonable utilization of Yunnan laterite ore. (C) 2017 Elsevier B.V. All rights reserved.
查看更多>>摘要：The instalment of packed fluid guiding media in the cyclonic-static micro-bubble flotation column (FCSMC) has been experimentally tested for improving flotation efficiency. This paper presents calculations of the hydrodynamics of the continuous phase only in the FCSMC columns, obtained using computational fluid dynamic (CFD) with a single-phase model. The flow characteristics in the open and packed FCSMC columns are compared and interpreted in relation to the enhancement in the flotation recovery. In the open column, a mono-turbulent circulating flow pattern formed in the whole column. In comparison to the flow field in the open FCSMC, the flow pattern in the FCSMC packed with the fluid guiding media changed from a strong cyclonic flow to a mild upward flow in the column separation part so as to avoid particle-bubble detachment. The packed media is capable of maintaining a strong cyclonic flow in the cyclone separation part so that the particles collide with, and attach to, the bubbles, while stabilizing the liquid flow in the column separation part so that the attached particles stay attached to the bubbles. The influence of the rotating flow on the particle-bubble detachment was quantified by considering a partide-bubble couplet in the flotation column. The probability of particle detachment is substantially decreased in the packed column as the rotating velocity is dramatically decreased due to the hindrance effect of the packed media. The Bond number of the couplet in the open and packed columns is 0.59 and 0.15 individually, corresponding to the probability of particle detachment 51% in the open column and 034% in the packed column. In particular, we have connected the hydrodynamics to particle-bubble detachment in order to understand the mechanism for the improvement of the flotation recovery in the packed FCSMC flotation column. Computer simulation and modeling is proved to be a powerful tool in mineral processing research where experimental techniques are restricted due to the limitations of experimental conditions. (C) 2017 Elsevier B.V. All rights reserved.
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