A new oxalic acid (H2C2O4) and hydrogen peroxide (H2O2) based extraction process was developed to recover valuable metals in particular Ga and Ge from the zinc refinery residues. H2C2O4 and H2O2 leaching studies indicated that the selective leaching of metals in the residues, that primarily contain Zn, Cu, Fe, SiO2, Ga and Ge, can be achieved. Under the optimal leaching conditions ([H2C2O4] = 110 g/L, [H2O2] = 0.12 mol/L, L/S ratio = 8, T = 40 °C and t = 30 min), 99.32% of the Ga, 98.86% of the Ge and 30.25% of the Fe were leached out, whereas the leaching of Zn, Cu and Si only reached 0.30%, 0.82% and 0.43%, respectively. Concerning leachate purification, 98.31% of the iron could be removed in the form of FeC2O4·2H2O with minor losses of Ga and Ge (1.08% and 0.68%) using an ultrasound-assisted iron powder replacement method under optimal conditions. The Ga (99.36%) and Ge (99.89%) were subsequently extracted by tri(octyl-decyl)amine (N235). After extraction, the loaded organic phase was stripped of Ga (98.91%) and Ge (99.21%) into separate solutions using sequential treatments of 2 mol/L H2SO4 and 4 mol/L NaOH respectively. Based on these results, a process flow sheet of efficient separation and recovery of Ga and Ge is presented.
Enrichment and migration regularity of coal particles in compound force field provided by Falcon concentrator were studied. Influence of centrifugal force and fluidization water pressure on the distribution rates and ash contents of materials that enriched in overflow, top separation area and bottom separation area were tested respectively. Radial velocity of fluidization water, having an important influence on the sedimentation of particles, was calculated and results show that radial velocity of fluidization water in top groove is greater than that in bottom groove, which contributed to the selectivity and recovery of combustible. Besides, density composition of products in different enrichment areas was studied. Results show that in the upward migration process, particles with high density are gradually captured. Therefore, the material density is gradually reduced from bottom to top separation area. Meanwhile, mismatch phenomena occurred as the existence of heavy particles in overflow, and light particles in the grooves. Based on the morphology analysis, it is can be deduced that particles mismatch is the results of the increase of drag coefficient since the irregular shape.
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.
An experimental study is conducted to investigate the effect of filling interval time (FIT) on the uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of cemented coarse tailing backfill (CCTB). A total of 72 CCTB samples with diameter×height of 50mm×100mm prepared at different solid contents (70, 72, and 75wt%) and water-to-cement ratios (3.00, 2.72, and 2.33) were subjected to UPV and UCS tests at 12, 24, 36 and 48h of FIT. The UCS and UPV values of the CCTB samples increased with the increase in the solid content. However, an increase in FIT led to a decrease in the UPV and UCS of the CCTB samples. Different types of curve fittings were conducted to obtain the correlation between UPV and UCS versus FIT at different solid contents. A polynomial function can explain the relationship between UPV and FIT. Moreover, the UCS and UPV values exhibit a linear function. CCTB also shows a failure mode of tensile failure-tensile shear failure transition-tensile and shear mixing failure modes, which provides a theoretical basis for the strength design and stability control of backfills.
Flotation, which exploits the differences in the surface wettability of minerals to effect separation, has been crucial in rare earth elements (REE) beneficiation. Monazite, a phosphate mineral commonly containing REE (typically lanthanum, cerium, and neodymium), occurs in association with hematite and quartz gangue minerals in some low grade deposits. In this study, the physicochemical properties including contact angle, zeta potential, and floatability of monazite, hematite, and quartz were determined in the presence of oleic acid as a collector. Contact angle measurements indicated adsorption of oleic acid onto the minerals' surfaces. Zeta potential measurements were used to elucidate oleic acid adsorption mechanism onto the mineral particle surfaces. Results from zeta potential measurements indicated that depressants are required to achieve selective flotation recovery of monazite from hematite and quartz. The flotation test results confirmed poor selectivity between monazite; and hematite and quartz, respectively. However, rare earth oxides (REO) in monazite floated better than both hematite and quartz at all the oleic acid dosages investigated. The use of sodium silicate and starch as depressants enhanced the selective flotation recovery of REO from hematite and quartz mixtures.
In the present work, emulsion liquid membrane (ELM) is investigated to select the suitable conditions for extraction of Co (II) ions from acidic chloride solutions using Cyanex 301 as extractant. The effects of extractant and surfactant concentrations, mixing speed, concentration and type of stripping solution, phase ratio, treatment ratio, and nature of diluent on the extraction rate were studies. Under the optimum conditions, extraction of cobalt in competition with nickel has been also studied for different feed mixture solution. Solvent extraction and stripping of cobalt and nickel in mixture was first carried out in order to have an idea about this extractant. Solvent extraction results show that almost 99% of cobalt and nickel are extracted with 0.1M Cyanex 301 at pH above 2 within 2min. However, Based on the stripping process, it was possible to separate cobalt and nickel at low acid concentration (0.5M) with separation factor of 502. ELM results show that under the optimum conditions, the system is selective for cobalt than nickel, especially within the first minutes of all experiments.
In this research, a numerical approach and a series of laboratory tests have been used to investigate the effect of vertical baffling and height to diameter ratio on the axial mixing in flotation columns. The baffle is a plate located perpendicular to the cross section of the column with a length of 2.8m and thickness of 0.4cm. The computational domain is a column with a circular cross section having a height of 3.2m and a diameter of 10cm. Three-dimensional simulations were executed using Eulerian two-phase computational fluid dynamics (CFD) models for both non-baffled and baffled columns. In order to reduce computing demand and simplify the problem, it was assumed that the column is already filled with water, and air enters from the lateral and upper surfaces of a cylindrical sparger with a length of 15cm and a diameter of 1cm located vertically at the bottom of the column. To validate the simulation results, a series of laboratory flotation column experiments have been performed under the above-mentioned conditions. Three-dimensional simulations were executed using an Eulerian two-phase model for both non-baffled and baffled columns. The simulated pressure values on the wall at 0.2m and 2.8m height of the non-baffled column were in good agreement with experimentally measured values with the highest relative difference of <3.07%. Comparison of the computational results for the non-baffled and baffled columns showed that baffling can reduce water axial velocity up to 16.96%, which consequently reduces the axial mixing in the column and increases flotation recovery. Study of the effects of height to diameter ratio showed that effect of baffling in columns with lower aspect ratios is more prevalent for reducing the axial mixing.
The underground separation of gangue from coal is an important part of the process of reducing transportation costs and improving production efficiency. A new method is proposed in this paper to separate gangue from coal on the basis of density, calculated from volume using three-dimensional (3D) laser scanning technology. This approach is based on the laser triangulation method and weight. Taking into account the weigh-in-motion technology that is currently widely applied, the main objective of this approach is to determine the volume of the object being measured. Thus, the principles of 3D laser scanning and laser triangulation were studied in detail and a relative formula was deduced. The reasons and solutions for possible errors are also analyzed in this paper, depending on the method applied to measure volumes of gangue and coal. Physical relationships of objects to be measured, as well as laser and measuring data planes are also presented, depending on principles of 3D laser scanning. A parameter selection method is presented to determine the appropriate photoelectric recognition device to use for coal or gangue, while error due to voids between objects was measured, and transportation belts analyzed. The assumption put forward in this study is that the ratios of voids between objects, transportation belt, and the exact volume of objects all conform to a normal distribution; this was shown to be the case by both experiments and statistical theory. A mathematical model was therefore constructed that is suitable for the recognition of coal and gangue based on this theory, while algorithms of recognition threshold values and identification rate are presented.
It is well accepted that non-polar oils can be used as collector extender in oil agglomeration flotation of many different types of mineral. In this paper, in order to study the influences of oil structures on the non-polar oil assisted dodecylamine (DDA) flotation of quartz, the research focuses on the interaction of DDA (collector) and non-polar oil (collector extender) in aqueous phase. In this work, saturated hydrocarbon dodecane and cyclohexane, unsaturated hydrocarbon dodecene, aromatic hydrocarbon dimethylbenzene and 1-methylnaphthalene were chosen as researched subjects, and the influences of oil structures on interfacial activity of oil–DDA–water ternary models were investigated by experimental and theoretical methods. The flotation results demonstrated that the collecting capability of the oil and DDA combination follows the order of 1-methylnaphthalene>dimethylbenzene>dodecene>cyclohexane>dodecane. Moreover, molecular dynamic (MD) simulation is performed to investigate the interfacial property of these five non-polar oil-DDA-water systems, and five parameters, radial distribution functions, interaction energy, density distribution, interfacial thickness and self-diffusion coefficient are proposed to reveal the influence mechanism of molecular structure on interfacial activity of the ternary oil-DDA-water systems. The same trends are obtained from the parameters described above, aromatic hydrocarbon dimethylbenzene and 1-methylnaphthalene performance better than saturate hydrocarbon and unsaturated hydrocarbon. The researched results indicate the interaction between non-polar oil and DDA hydrophobic alkyl tail would enhance the mobility of oil component, which induce significant change of interfacial thickness and diffusivity. Additionally, the interaction between DDA hydrophilic head group and water molecules via strong hydrogen bonds, van der Waals interactions and weak electrostatic attraction would lead to water molecules penetrate through DDA monolayer and adsorb on oil surface. The researches enable us to obtain a deeper microscopic-level understanding of the interaction between oil-DDA-water ternary components, and maybe have some references for designing of oil-assisted flotation agent.
The pressure oxidation process to prepare sodium pyroantimonate from sodium thioantimonite solution was optimized. The results indicate that increasing reaction temperature, oxygen partial pressure and stirring speed can significantly accelerate the oxidation precipitation rate of Sb. A decrease in Sb3+ concentration is beneficial for shortening the reaction time. The NaOH concentration has no significant effect on the oxidation velocity but plays an important role in the quality of sodium pyroantimonate. An increase in stirring speed and oxygen partial pressure result in the formation of a red precipitation in the solution with 12.5g/L of NaOH, while the desired sodium pyroantimonate can be produced with a NaOH concentration of 30.0g/L. The XRD and SEM-EDS analysis confirm that the red precipitate is composed of NaSb(OH)6 and Na6Sb4S9.
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.After 30 min of exposition the MIC of organovermiculite samples before and after stability test were the same for Staphylococcus aureus and Escherichia coif with value 333 (%; w/v) and the MIC decreased to 0.014 (%; w/v) with longer time of exposition (120 h). A small difference was observed at Enterococcus faecalis where MIC was 10 (%; w/v) after 30 min of exposition for the sample after stability test in neutral pH. However, after 24 h of treatment the MIC value decreased to 0.014 (%; w/v). And finally, bacterial strain Pseudomonas aeruginosa showed a great resistance against antibacterial organovermiculite samples and MIC did not decreased under 10 (%; w/v) even after 5 days of exposition. (C) 2016 Elsevier B.V. All rights reserved.
The application of coal fly ash magnetic spheres (MSs) in water treatment is limited due to their complex mineral compositions, low magnetism, and large diameters. In this study, MSs were carefully ball milled and magnetically separated to improve their related properties. After the processing, the resultant magnetic ball-milled MSs (MBMSs) show a substantial change in composition, magnetism, and surface property in addition to a decrease in diameter. Compared with those of the original MSs, the Fe percentage, magnetism, and specific surface area of MBMSs are increased by 25.87%, 54.60%, and 810%, respectively. Dispersive spectrometer mapping investigation shows segregated high- and low-Fe areas with different structures in MS. These different structures enable purification. Highly turbid clay water flocculation experiments using MSs as flocculants indicate that MBMSs can cause fast flocculation whereas the compared samples exert less or slight flocculation effect. Zeta potential investigation suggests that the different flocculation effects are due to the change in the point of zero charge (pHPZC). The pHPZC increases from 3.91 for the original MS to 4.96 for MBMS. The reduction in the diameter, as well as the increase in magnetism, surface area, and pHPZC, makes MSs applicable to water treatment.
Flotation separation of scheelite from calcite is difficult due to the similarities in their surface properties. In this work, the flotation behavior of scheelite and calcite using oxidized paraffin soap (OPS), benzohydroxamic acid (BHA) and the mixed OPS/BHA collectors was investigated through micro-flotation experiments. The flotation results of single mineral experiments demonstrated a higher selectivity for the flotation of scheelite from calcite at pH9 than individual OPS and BHA when using water glass as depressant. In order to probe the validity of the findings, mixed binary minerals experiments, contact angle and zeta potential experiments were also carried out successfully.
Collophane is an important phosphate mineral, which has proven to be difficult to float from gangue. In this work, the novel application of reactive oily bubbles to enhance collophane flotation is reported. Three different types of bubbles, conventional air bubble, oily bubbles (kerosene only) and reactive oily bubbles (kerosene containing fatty acids) approaching collophane particles were studied by measurements of zeta potential, induction time and contact angle. The reactive oily bubble shows negligible effects on the zeta potential of collophane particles. A shorter induction time of reactive oily bubble was found at pH6.0 and/or at pH9.0 relative to the conventional air bubbles and the oily bubbles. This suggests a strong collection power of reactive oily bubble. Advancing contact angles of the reactive oily bubble on collophane increased dramatically with pH. At pH9.0, a contact angle of 120 degrees was observed where the reactive oily bubble flotation is anticipated. Micro-flotation results demonstrate the superiority of reactive oily bubbles over air bubbles for collophane flotation. A concentrate containing 35.67% of P2O5 and 0.39% of MgO was obtained using reactive oily bubble flotation at pH9.0. Micro-flotation results also show that Ca2+ and Mg2+ ions have a negative effect on the collophane flotation, but the effect of reactive oily bubble system is smaller than that of air bubble system.
The carbothermic reduction behavior of original ilmenite and pre-oxidized ilmenite concentrates were investigated by a non-isothermal method using a thermogravimetry facility. The reaction degree was calculated using the tail gas composition and the Starink method to analyze the activation energy of the reduction. The results demonstrated that trends of different reaction degree curves are similar under the same conditions. The average activation energy of the pre-oxidized ilmenite concentrate was less than that of the original form by approximately 25%, and the starting reduction temperature was lower by 67K than that of the original ilmenite concentrate. However, the reduction time of the pre-oxidized ilmenite concentrate was longer than that of the original ilmenite concentrate for the same reaction degree; therefore, a slow reduction rate for the oxidization sample was observed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS) were used to characterize the phase and micro-morphology of the two raw materials and compare the reduction products.
In this study, the effect of sodium chloride on the flotation of a fine coal sample was investigated. The results indicated that flotation of coal was highly dependent on changes in sodium chloride concentration. An increase in the sodium chloride concentration resulted in increases in the combustible recovery as well as concentrate ash content. The froth stability and particle size distribution in the slurries with different sodium chloride concentrations were measured. The results showed that the increase in froth stability and enlargement in particle size were both favorable for the recovery of coal particles in flotation. The underlying mechanism was investigated by examining the zeta potential of pure coal particles and pulp rheology. The pulp rheology measurements clearly indicated that changes in froth stability were attributed to changes in slurry viscosity, which ultimately enhanced the recovery of coal particles. The decrease in zeta potential was responsible for the increase in particle size in slurries due to particle coagulation, which is caused by a decrease in electrostatic repulsion among the particles.
The main purpose of this study is to investigate the effect of reaction temperature and NH4HCO3 on the overall performance of a pH swing mineral carbonation. The overall performance of the pH swing process is investigated in terms of carbonation efficiency and product purity. Initially, 2M H2SO4 is used for red gypsum dissolution at 70°C. Then in the second stage, NH4OH is added for increasing the solution pH and removing the impurities from solutions. Finally, CO32– is introduced to calcium rich solution in the form of pure CO2 and NH4HCO3. The experimental results show that using NH4HCO3 improves carbonation efficiency and product purity. Carbonation efficiency attains a maximum value at 75°C and then decreases gradually with increasing temperature up to 300°C, with both CO2 and NH4HCO3. In this research, CaCO3 with the maximum purity of 99.05% is produced successfully when NH4HCO3 is used as a CO32– source.
This paper introduced dextran sulfate sodium, a medical intermediate rich in sulfate group, as a potential depressant for calcite and fluorite in scheelite flotation. The flotation behaviors of scheelite, calcite and fluorite under different pulp pH with dextran sulfate sodium acting as depressant and sodium oleate acting as collector were studied through micro-flotation tests. The results showed that when sodium oleate was used alone, the three minerals floated well and were difficult to separate. Dextran sulfate sodium exhibited a selective depressant effect on calcite and fluorite flotation when it was added before sodium oleate. Using dextran sulfate sodium as depressant could achieve the preferential flotation separation of scheelite from calcite and fluorite by control of pulp pH at 7.0. The selective depressant effect of dextran sulfate sodium on calcite and fluorite was explored through surface analyses including zeta potential measurements, contact angle measurements and FTIR studies on mineral samples treated with dextran sulfate sodium and/or sodium oleate. On the basis of the surface analyses, a selective adsorption model of dextran sulfate sodium on calcite and fluorite was proposed.
A systematic study of diasporic bauxite flotation using commercial oleic acids with different iodine values as collector was conducted in this paper. Bench scale flotation tests for diasporic bauxite ore and micro-flotation tests for relevant pure minerals (including diaspore, pyrophyllite and kaolinite) were carried out at different conditions using commercial oleic acids with iodine values of 65, 121 and 131. The results suggest that an increase in the iodine value of oleic acid would lead to improved flotation separation of diaspore from aluminosilicates. Use of the commercial oleic acid with iodine value of 131 in closed-circuit flotation tests allowed us to obtain a concentrate with alumina-to-silica (A/S) ratio of 5.33 and alumina recovery of 85.56% from the feed ore (A/S ratio=3.39). Chemical analyses of these commercial oleic acids found that an increase in the iodine value was associated with increased proportion of linoleic acid in the commercial oleic acids. To fundamentally understand the correlation between the iodine value of commercial oleic acids and the efficiency of flotation separation of diaspore from aluminosilicates, the computational studies of frontier molecular orbital energy of oleic and linoleic acid were done, and the results suggest that linoleic acid has higher chemical activity than oleic acid and its chemical adsorption on diaspore is more stable than that of oleic acid.
