Search

This study investigated the effects of H2O2 treatment on xanthate interaction and flotation separation of chalcopyrite and pyrite by making use of a series of laboratory flotation experiments and surface analysis techniques. Flotation test results showed that H2O2 treatment influenced the flotation behaviors of the two minerals; however, flotation of pyrite was depressed more significantly than that of the chalcopyrite. Under well-controlled H2O2 concentration, the selective separation of chalcopyrite from pyrite was realized at pH 9.0, at which the recovery of chalcopyrite was over 84% and that of pyrite was less than 24%. Zeta potential, UV−visible and IR spectrum measurements revealed that the collector interacted differently with the two minerals after H2O2 treatment, and the surface of chalcopyrite adsorbed much greater amount of xanthate than that of the pyrite. IR and XPS analyses showed that the H2O2 treatment significantly changed the surface properties of pyrite to very hydrophilic species that inhibited the adsorption of collector and thus depressed the floatability of pyrite. While, the surface of chalcopyrite remained mildly inert to H2O2, as a result, the adsorption of xanthate and its oxidation to dixanthogen were very effective, which enhanced the flotation of chalcopyrite.

The traditional acid leaching process for releasing valuable metals from spent lithium-ion batteries (LIBs) is inefficient and inevitably consumes large amounts of reductants. In this study, a novel process, based on a reduction thermal treatment and reductant-free acid leaching, for recycling valuable metals from spent LIBs has been developed. First, a thermodynamics calculation was performed to judge whether the reducing reaction between LiCoO2 and graphite can occur or not. Then, reduction thermal treatment experiments were conducted. The process was tested by a thermogravimetry/differential thermal analysis method, and reaction products were measured by X-ray powder diffraction and X-ray photoelectron spectroscopy. The experimental results agree well with thermodynamics analysis, and the desired CoO and Li2CO3 were obtained under the optimum processing conditions of 600 °C, 120 min, and molar ratio of LiCoO2 to graphite of 2:1. Finally, almost 100% Li and Co were easily leached from the reaction produ...

This study investigated the promotion effect of A. ferrooxidans on complex heavy metals coprecipitation process. A. ferrooxidans significantly enhanced the ferrous oxidation, which also promoted the formation of iron-oxyhydroxysulphate. Cu(II) concentration reduced to 0.058 mmol/L in A. ferrooxidans inoculated system, and Cd also reduced to the lowest concentration (0.085 mmol/L). Pb was mainly immobilized as anglesite and iron-oxyhydroxysulphate promoted the removal of remanent Pb in solution. The precipitates are characterized by XRD, SEM, and FTIR analysis. The main component of the iron-oxyhydroxysulphate was well crystallized jarosite. A. ferrooxidans contributed to the formation of schwertmannite in later monovalent cation lack stage. Higher ferrous iron oxidation rate and Fe(III) supply rate in A. ferrooxidans inoculated system facilitated polyhedron crystal formation and the increase of particle diameter. Complex heavy metals could be incorporated into iron oxyhydroxysulphate crystal, and efficiently removed from acidic wastewater through A. ferrooxidans mediated coprecipitation.

The effect of octanol in cassiterite flotation using benzohydroxamic acid (BHA) as a collector was investigated. The adsorption mechanism of octanol and BHA on the surface of cassiterite was analyzed by adsorption experiments and infrared spectra analysis. Micro-flotation results indicated that single octanol exhibited almost no collecting power to cassiterite over a wide pH range. However, as an auxiliary collector, octanol could markedly decrease the consumption of collector BHA and keep the recovery of cassiterite in high level. The results of adsorption experiments and infrared spectra demonstrated that single octanol was not adsorbed on the surface of cassiterite. It formed adsorption connected with BHA on the surface of cassiterite, and enhanced the hydrophobicity of cassiterite. Octanol promoted the adsorption amount of BHA on the cassiterite surface, and decreased the consumption of BHA.

Systematic multiple spurious operation review is the important basement of Fire PSA Component Selection and Fire Induced Risk Modeling. It is a task of systematically evaluation of all plant systems and identification of equipments susceptible to potential spurious actuation that may challenge safe shutdown capability via spurious operations, which can ensure that the fire PSA model addresses the impacts of single spurious operations (SSOs) and multiple spurious operations (MSOs). In this paper, different methodologies of systematic multiple spurious operation review are studied and it is found that two methodologies are given in literature published at home and abroad: one methodology is development of comprehensive plant specific MSO list by panel review. This methodology is based on generic list of MSOs combined with plant specific information review. This methodology proposes high requirements for the expert panel and hard to avoid missing of some scenarios. Another methodology is review of all plant systems and components to receive SSOs, and then using MSO matrix to evaluate and encode each unique pair to receive MSOs that disable the system function. This methodology can ensure the integrity of MSO list, but the matrixes are too complicated. In this paper, the fault tree method is employed to improve the matrix method in the MSO evaluation process of the latter methodology. Reactor Coolant System (RCS) is taken as an example to describe the application of this method to CAP1000. Engineering practice shows that the fault tree method can effectively avoid omissions of MSO scenarios, and it is more useful and simple for tertiary or quaternary MSO evaluation, as well as more convenient for further MSO evaluation due to cross system issues. Furthermore, MSO fault trees can be directly called by fire PSA model for evaluation, which can lay a foundation for the follow-up work of fire PSA.

Effects of particle size and chain length on flotation of quaternary ammonium salts (QAS) onto kaolinite have been investigated by flotation tests. Dodecyltrimethylammonium chloride (DTAC) and cetyltrimethylammonium chloride (CTAC) were used as collectors for kaolinite in different particle size fractions (0.075 ~ 0.01 mm, 0.045 ~ 0.075 mm, 0 ~ 0.045 mm). The anomalous flotation behavior of kaolinite have been further explained based on crystal structure considerations by adsorption tests and molecular dynamics (MD) simulation. The results show that the flotation recovery of kaolinite in all different particle size fractions decreases with an increase in pH. As the concentration of collectors increases, the flotation recovery increases. The longer the carbon chain of QAS is, the higher the recoveries of coarse kaolinite (0.075 ~ 0.01 mm and 0.045 ~ 0.075 mm) are. But the flotation recovery of the finest kaolinite (0 ~ 0.045 mm) decreases with chain lengths of QAS collectors increasing, which is consistent with the flotation results of unscreened kaolinite (0 ~ 0.075 mm). It is explained by the froth stability related to the residual concentration of QAS collector in mineral pulp. In lower residual concentration, the froth stability becomes worse. Within the range of flotation collector concentration, it’s easy of CTAC to be completely adsorbed by kaolinite in the particle size fraction (0–0.045 mm), which led to lower flotation recovery. Moreover, it is interesting that the coarser particle size of kaolinite is, the higher flotation recovery is. The anomalous flotation behavior of kaolinite is rationalized based on crystal structure considerations. The results of MD simulations show that the (001) kaolinite surface has the strongest interaction with DTAC, compared with the (001) face, (010) and (110) edges. On the other hand, when particle size of kaolinite is altered, the number of basal planes and edge planes is changed. It is observed that the finer kaolinite particles size become, the greater relative surface area of edges and the more the number of edges are. It means that fine kaolinite particles have more edges to adsorb fewer cationic colletors than that of coarse kaolinite particles, which is responsible for the poorer floatability of fine kaolinite.

Extracellular polymeric substances (EPS) produced by acidophilic bioleaching microorganisms play an important role in the production of acid mine drainage and metal sulfide bioleaching. EPS mediate the contact between microbial cells and growth substrates, having a pivotal role in organic film formation and bacterium-substratum interactions. The production and chemical composition of EPS produced by seven bioleaching strains grown with different substrates were studied. Analysis of the EPS extracted from these strains indicated that the EPS consisted of carbohydrates, proteins and galacturonic acid. The contents of EPS, carbohydrates, proteins and galacturonic acid of EPS were largely related to the kind of strain used and culture condition. The results show that EPS productions of microbes grown with pyrite were significantly higher than those of microbes grown with sulfur or FeSO4·7H2O. The highest EPS production of the seven acidiphilic strains was (159.43±3.93) mg/g, which was produced by Leptospirillum ferriphilum CBCBSUCSU208015 when cultivated with pyrite.

The effect of electrolyte on settling behavior of kaolinite was studied. Effects of hard water on selective flocculation of diasporic bauxite was tested and the measures were taken to eliminate the effects of Ca2+ and Mg2+ in hard water. The results indicated that, not only the concentration of electrolyte ions but also the ionic valence of the electrolyte ions affects the settling behavior of kaolinite; hard water significantly affects its selective flocculation owing to Ca2+ and Mg2+; general dispersants could not eliminate the effects of Ca2+ and Mg2+. Self-made softening agent in our lab could weaken or eliminate the effects of hard water on flocculation processes. The results of molecular dynamics simulation show that softening agent molecules could restrict Ca2+ and prevent them from playing their roles, so as to eliminate the effects. The continuous pilot experiment results of bauxite flocculation were even better than those obtained in laboratory.

Aluminum tri-polyphosphate was synthesized from bauxite tailings and phosphoric acid with a P/Al molar ratio of 3. This is highly advantageous from a waste recycling perspective as bauxite tailings are generally regarded as unusable waste. The acidity, whiteness and mean particle size of prepared aluminum tri-polyphosphate are all improved after modification. The possibility of using modified aluminum tri-polyphosphate as an anticorrosive pigment was also investigated by electrochemical impedance spectroscopy. The resistance of the coatings with modified aluminum tri-polyphosphate is 7×107 Ω for 40 d of immersion, which is superior or at least comparable to that of coatings containing APW-2, which exhibits a resistance of 5.7×107 Ω.

The flotation and adsorption behaviors of dodecyltrimethylammonium chloride(DTAC) and cetyltrimethylammonium chloride(CTAC) on diaspore and kaolinite were studied. Solution depletion methods were used to determine adsorption isotherms. Fluorescence probe test along with Zeta potential measurement was also conducted for further investigation into the adsorption of quaternary amines at the mineral-water interface. The results show that the flotation recovery of kaolinite decreases with an increase in pH when DTAC and CTAC are used as collectors, while diaspore is on the contrary. As the carbon chain length of the collectors increases, the flotation recoveries of minerals increase. However, the increment rate of kaolinite is significantly lower than that of diaspore. In the low surfactant concentration range, the cationic surfactants adsorb readily on diaspore surfaces just due to electrostatic interactions. As for kaolinite surfaces, ion exchange process also exists. With a further increase in surfactant concentration, the adsorption was ascribed to the hydrophobic association of chain-chain interactions. Micro-polarity of mineral surfaces study shows that CTAC has a better hydrophobic characteristic than DTAC. Larger aggregates are formed with CTAC on diaspore than on kaolinite in the same solution concentration. The results also indicate that the chain length of cationic surfactants has a greater influence on the adsorption of diaspore than on kaolinite, which is consistent with the flotation result.

The collecting power of tertiary amines (DRN, DEN and DPN) on kaolinite follows the order of DEN>DPN>DRN. After reacting with DRN, DEN and DPN, the surface potentials of kaolinite increase remarkably, and the recruitments caused by collectors also follow the order of DEN>DPN>DRN. The results of dynamics simulation show that the geometries of substituent groups bonding to N are deflected and twisted, and some of bond angles are changed when tertiary amines cations adsorb on kaolinite (001) surface. Based on the results of dynamics simulations and quantum chemistry calculations, the electrostatic forces between three tertiary amines cations and 4×4×3 (001) plane of kaolinite are 1.38×10 −7 N (DRN 12 H + ), 1.44×10 −6 N (DEN 12 H + ), 1.383×10 −6 N (DPN 12 H + ), respectively.

The flotation of diaspore and kaolinite by one of a series of tertiary amines (DRN, DEN, DPN and DBN) was investigated. The tertiary amines show better floating recovery for kaolinite compared to diaspore. The maximum recovery D-value is 45% over a pH range from 3 to 8. FT-IR spectra confirm the presence of hydroxyl groups on the surface of kaolinite and diaspore. Zeta potential measurements show that the mineral surfaces are negatively charged over a wide pH range. Ionization of hydroxyl groups mainly accounts for the surface charging mechanism. The adsorption of tertiary amines onto the mineral surface is due mainly to electrostatic effects and the difference in electrostatic effect between a collector and the two minerals can explain the flotation separation. Inductive electronic and steric effects from the substituent groups result in different collecting powers for the four tertiary amines.

FCLS (Ferric Chromium Lignin Sulfonate) was used to aid the separation of chalcopyrite from marmatite. Flotation, adsorption and zeta-potential tests of treated marmatite and chalcopyrite were performed. The flotation of marmatite was strongly depressed, while that of chalcopyrite was only slightly depressed, over a wide range of pH values when FCLS was used as depressant in the presence of Butyl Xanthate (BX). The adsorption of BX onto chalcopyrite or marmatite takes place over a wide pH range. The adsorption density of BX on chalcopyrite and marmatite decreases as the pH increases. The adsorption density of FCLS onto marmatite is greater than the adsorption density onto chalcopyrite. The zeta potentials of chalcopyrite and marmatite become more negative due to the addition of xanthate and FCLS.

The influence on fine particle aggregation and flotation behavior induced by high intensity conditioning (HIC) from saturated of the slurry with CO 2 saturation was investigated. Bubble size measurements were conducted. The effect of dissolved gas, xanthate addition and agitation speed on fine sphalerite particle aggregation- and flotation-behavior were studied. The results show that during HIC in air or CO 2 saturated water xanthate acts as a frother. The dissolved gas content in the pulp and HIC play a synergistic role in promoting fine particle aggregation and hence flotation; a significantly enhanced aggregation of fine sphalerite particles in a CO 2 saturated slurry by HIC is observed. The aggregate size increased when the agitation speed was increased from 700 r/min to 1500 r/min. Increasing the HIC speed to 1500 r/min caused a positive impact on flotation kinetics. Further increasing the speed to 2000 r/min resulted in an adverse effect on flotation kinetics.

A special experiment setup was designed to observe the interaction between bubbles and particle in flotation cell and to analyze the bubble characteristics such as bubble size, distribution and bubble-loading efficiency. Bubbles in water-gas system and three-phase system were measured. The results indicate that with the current setup the bubbles as small as 10 µm can be easily distinguished. The average size of the bubbles generated under the given conditions in two-phase system is 410 µm at frother concentration of 0.004%, which is in good correspondence with the results of other works. The effect of frother on bubble size was probed. Increasing frother concentration from 0 to 0.004% causes a reduction of bubble size from 700 to 400 µm. The bubble loading efficiency was reported. The result indicates that the fine particle is more easily entrapped than the coarse particle. Some factors, which have effect on measurement accuracy were discussed. The aeration speed has a significant effect on the accuracy of results, if it surpasses 30 mL/s, and the image becomes unclear due to the entrapment of fine particle. Another factor, which can affect observing results, is the sampling position. At a wrong sampling position, the images become unclear.

In order to offer high grade concentrate to produce alumina by Bayer, the reverse-flotation technology of bauxite was investigated. The results show that sodium hexmetaphosphate has different depression on the flotation of diaspore and kaolinite. The recoveries of diaspore decrease markedly with the increase of the concentration of sodium hexmetaphosphate with dodecyl-amine as collector. Fourier transform infrared spectra indicate that the absorbance band 875 cm−1 of the asymmetric stretching vibration of bridge oxygen P-O-P shifts to 880 cm−1, and the 1 264 cm−1 of the asymmetric stretching vibration of the bridge PO2 shifts to 1 267 cm−1 in the diaspore’s spectra. This demonstrates that sodium hexmetaphosphate interacts through bridging PO2 groups with the Al atoms exposed on the diaspore and kaolinite surfaces to form P-O-Al bond. Adsorption measurements also testify that sodium hexmetaphosphate adsorbs easily on the surface of diaspore. The adsorption density of PO3− on the surface of diaspore is about 4.7 × 10−6 mol/m2, while that on the kaolinite is only about 3.5 × 10−7 mol/m2 when pH value is 6.

Pyrite (FeS2) bulk and (100) surface properties and the oxygen adsorption on the surface were studied by using density functional theory methods. The results show that in the formation of FeS2(100) surface, there exists a process of electron transfer from Fe dangling bond to S dangling bond. In this situation, surface Fe and S atoms have more ionic properties. Both Fe2+ and S2− have high electrochemistry reduction activity, which is the base for oxygen adsorption. From the viewpoint of adsorption energy, the parallel form oxygen adsorption is in preference. The result also shows that the state of oxygen absorbed on FeS2 surface acts as peroxides rather than O2.

Flotation tests show that the floatability of kaolinite is much better in an acidic than in an alkaline medium containing cationic collectors. The (0 0 1) basal planes of kaolinite are found to adsorb cationic collectors favorably, which render the surface hydrophobic. The (0 0 1) planes interact with macromolecules carrying groups containing –O–, –N–, and/or –F– of high electronegativity, and the resultant flocculation minimizes the exposure of hydrophilic (0 0 1) planes. As a result, the cationic flotation of kaolinite is enhanced by the addition of these types of macromolecules. The zeta potential measurement and macromolecule adsorption study indicate that the adsorption of anionic PAM on kaolinite is dominated mainly by hydrogen bonding interactions.

The geometry and the electronic structure of the stoichiometric FeS2(1 0 0) surface have been studied by using density-functional theory (DFT) method. The (1 0 0) surface is very stable, does not give any significant geometric relaxation and can be regarded as simple termination of the bulk structure along a plane of cleaved Fe–S bonds. The electronic structure at the (1 0 0) surface shows rather differences compared to the bulk electronic structure. The electronic structure of FeS2(1 0 0) surface is characterized by surface states in the forbidden zone. The highest occupied and the lowest unoccupied states are localized at surface Fe sites.

Interactions of salt-type minerals with common inorganic flotation depressants were investigated through solution chemistry calculations. From the constructed conditional solubility product limits and the actual solubility product lines of calcium silicate and phosphate in fluorite, calcite, and apatite single-mineral systems, the critical precipitation pH or concentration of silicate and phosphate in the corresponding mineral suspensions was determined. These values provided a fundamental basis for interpreting the results of flotation tests and were in line with the results of ζ-potential and dispersant adsorption measurements. The surface precipitation of calcium silicate or phosphate on fluorite and calcite was identified as a major depression mechanism. Selective depressing conditions for different salt-type minerals using Na2SiO3 and Na3PO4 as depressants were determined on the basis of solution chemistry calculations of the systems.

The effects of silver sulfide (Ag2S) on the bioleaching of chalcopyrite and pyrite were investigated in this paper. It has been shown that Ag2S enhanced the yields of bioleaching of chalcopyrite but inhibited the bio-oxidation of pyrite. The addition of Ag2S selectively increased the copper dissolution from the chalcopyrite-containing ores in shake flasks with a recovery of 85.3% compared with 24.3% without Ag2S, while slightly decreased the iron yields from 51% to 41.8%. The copper extraction of the chalcoopyrite-containing waste rock in column leaching charged with 18 kg mass increased up to 21.7% in the presence of Ag2S, while only 3.4% in the absence of the catalyst. The mechanism of Ag2S catalysis could be explained well by the “Mixed potential model”.

The linear potential sweep voltammetry and electrochemical methods were used to study the mechanism and kinetics of gold dissolution in thiourea solution in the absence and presence of sodium sulphite. The results show that in the absence of sodium sulfite the dissolution rate of gold in thiourea solution is relatively slow and it increases with the increase of the concentration of thiourea and decreases with pH. Thiourea is easily oxidized to formamidine disulphide, which reduces the leaching efficiency and increases reagent consumption. In the presence of sodium sulphite, the effective concentration of thiourea is increased and the dissolution rate of gold in thiourea solution is greatly increased. The activation energy required for gold dissolution in thiourea solution with sodium sulphite is 20.9 kJ·mol−1 in the absence of sodium sulphite. It is evident that sodium sulphite has a significant effect on the electrochemical reaction kinetics of gold in thiourea solution.

Diaspore (α-AlOOH) was heated at various temperatures from 300 to 1 000 °C for 2 h. The alteration of diaspore by thermal treatment was investigated by differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The mechanism of thermal decomposition of diaspore was discussed according to the Coats-Redfern equation. It is found that after thermal treatment at 500 °C, diaspore is transformed entirely to corundum (α-Al2O3). Combined with the mass loss ratio obtained from the thermogravimetric analysis data, the activation energies for the thermal treatment of diaspore are calculated as Ea=10.4 kJ/mol below 400 °C and Eb=47.5 kJ/mol above 400 °C, respectively, which is directly related to the structural alteration of diaspore during the thermal treatment. The results indicate that the thermal decomposition of diaspore is conducted primarily by means of an interfacial reaction.

This paper presents some of the investigations of bioleaching and biooxidation applications in China. Bioleaching and biooxidation are new technologies with great potentials due to their simplicity, low operating cost, and little pollution to the environment. To date, two heap bioleaching plants and two biooxidation plants have been successfully put into operation to process copper ores and refractory gold concentrates, respectively. Investigations of applying bioleaching and biooxidation for other metal and non-metal resources are now being carried out.

Crushing and grinding, the prerequisite processes in many industries, are employed in areas such as minerals processing and powder technology. During these processes, minerals will cleave or fracture along specific crystal directions, where there are weak inter-planar bonds, generating exposed surfaces. On an exposed mineral surface, different ions can possess different numbers of broken bonds. The total number of broken bonds of all ions on the exposed surface can be considered as the number of broken bonds of the exposed surface. The broken bonds on the exposed surface make the latter more active and determine its reactivity. The broken bond density on the exposed surfaces of fluorite was calculated, enabling the anisotropic surface reactivity of fluorite such as surface energy, surface relaxation, dissolution, wettability, surface charge and adsorbability to be revisited. The results show that the surface broken bond density, which is related to the specific surface energy, could be used to predict the cleavage nature, surface relaxation degree, dissolution rate and surface stability of fluorite crystal. The distribution feature and the number of broken bonds of exposed active ions (such as Ca2+ for fluorite) can be used to predict and explain the anisotropic surface wettability and surface charge, as well as the adsorption mode and strength of organic molecule binding to different exposed surfaces. The calculation of surface broken bonds can serve as useful method to assess mineral surface chemical behavior. This approach is helpful for mineral/material chemistry research in general. Refereed/Peer-reviewed