A new extraction process of carbonaceous refractory gold concentrate

A new hydrometallurgical process for a carbonaceous refractory gold concentrate at ambient temperature and pressure was presented, including grinding-leaching, intensified alkaline leaching（IAL）, thiosulfate leaching and cementation by zinc powder. The experimental results show that the grinding-leaching and intensified alkaline leaching process result in the selective oxidation of arsenopyrite and pyrite. The oxidation ratio of As is 96.6%, and 46.7 % for S. The total consumption of NaOH in alkaline leaching is only 28 % of that theoretically calculated under the conditions of full oxidization for the same amount of arsenopyrite and pyrite transforming into arsenates and sulfates, and 83.6% of gold is synchro-dissoluted by thiosulfate self-generated during pretreatment. Since the carbonaceous matter in concentrate possesses a strong capability of preg robbing, the cyanidation process is not suitable for the extraction of gold after pretreatment. However, the gold leaching rate by thiosulfate leaching for 24 h is increased to 91.7% from 0 - 3.2% by ultra-fine grinding without the pretreatment. The recovery of gold by zinc cementation gets to 99.6%. Due to the thiosulfate self-generated during alkaline leaching, the reagent addition in thiosulfate leaching afterwards is lower than the normal one.     

Photoelectrocatalytic properties and reactivity of Ti/Au-TiO2 mesh electrodes

A kind of photoelectrode was innovated by anodising titanium mesh in H2SO4 solution and photo-reduced in HAuCl4 solution and named Ti/Au-TiO2 mesh electrode.The structural and surface morphology of the Ti/Au-TiO2 mesh was examined by X-ray diffraction,laser Raman spectra,scanning electronic microscopy(SEM) and X-ray photoelectron spectroscopy respectively.The results indicate that its crystal structure,morphology and the size of pore are affected greatly by gold deposition.XPS measurement show that the valence band of Ti/TiO2 has two peaks:a wide one at 4.97eV and a narrow one at 6.61eV,which correspond mainly to π(nonbonding)and σ(bonding)O 2p orbitals,The emission intensity of O 2p orbitals becomes stronger and the width of the valence band increases with the increase of Au content.And the emission of nonbonding shifts toward lower binding energy and that of bonding O 2p orbitals shifts toward higher binding energy.The photoelectrocatalytic(PEC) oxidation of humic acid( HA) was investigated in terms of TOC.The PEC oxidation efficiency of Ti/Au-TiO2 mesh with optimal content of gold is higher than that of Ti/TiO2 mesh.It is suggested that the recombination of electrons and holes is hindered owing to gold deposition.The investigation shows that PEC oxidation is a convenient way to mineralize organic matter for water treatment.     

Phase transformation in reductive roasting of laterite ore with microwave heating

Selective reduction of laterite ores followed by acid leaching is a promising method to recover nickel and cobalt metal, leaving leaching residue as a suitable iron resource. The phase transformation in reduction process with microwave heating was investigated by XRD and the reduction degree of iron was analyzed by chemical method. The results show that the laterite samples mixed with active carbon couple well with microwave and the temperature can reach approximate 1000 ℃ in 6.5 min. The reduction degree of iron is controlled by both the reductive agent content and the microwave heating time, and the reduction follows Fe2O3→Fe3O4→FeO→Fe sequence. Sulphuric acid leaching test reveals that the recoveries of nickel and iron increase with the iron reduction degree. By properly controlling the reduction degree of iron at 60% around, the nickel recovery can reach about 90% and iron recovery is less than 30%.     

Sulfuric acid leaching of low-grade refractory tantalum–niobium and associated rare earths minerals in Panxi area of China

By mineral liberation analyzer(MLA) automated quantitative system, the niobium–tantalum ore in this study was classified as refractory mineral of low-grade which was mainly composed of fergusonite, polycrase, ilmenorutile, and bastnasite. Most of niobium and rare earth metals were disseminated in these minerals(particle sizes of 95% rare earth elements40μm), which cannot be concentrated through traditional floatation process and treated by the current hydrofluoric acid leaching in industry application. It is necessary to develop a new approach to recovery these valuable metals. In this study, an improved method is proposed to extract these metals, which includes acid roasting and sulfuric acid leaching. The influence of mineralogy, acid concentration, leaching temperature, leaching time, and liquid to solid ratio was experimentally studied. It is observed that after the ground ore(-74μm) was roasted at 350 °C for 2 h with sulfuric acid(18.4 mol·L-1) in the ore to acid mass ratio of 1:1,and then the roasting residue reacted with 25% sulfuric acid at 90 °C for 2h, the recovery rate of rare earth elements reaches[90%, and the leaching extent of niobium can reach 84%.     

Study on the Recovery of Rhodium from Spent Organic Rhodium Catalysts of Acetic Acid Industry Using Pyrometallurgical Process

A new process recycling rhodium from organic waste containing rhodium in acetic acid industry is developed. Use the special affinity of base metal sulfides (FeS, Ni2S3 , CuS, etc.) on platinum group metals, adopting high nickel matte trapping-aluminothermic activation method to recovery rhodium from incinerator residue of organic rhodium waste. The method is shorter process, lower equipment requirement, and the higher activity of rhodium black. In pyrometallurgy enrichment process,the recovery rate of rhodium reached 94.65%, the full flow of rhodium recovery rate was 92.04%.     

Effects of citric acid on separation of sillimanite from quartz

Quartz is the main gangue mineral of sillimanite.The results show that Al^3 and Fe^3 ion can activate the floatation of quartz and make the separation of quartz and sillimanite difficult when anion collector is used,and citric acid can inhibit the quartz activated by metallic ion and have slight influence on the sillimanite.X-ray photoelectronic energy spectrum analysis indicates that there are obvious electronic energy peaks on the surface of the quartz before citric acid is added into the ore pulp in presence of Al^3 and Fe^3 ,and after citric acid is added,the energy peak vanished.So citric acid can make Al^3 and Fe^3 on the surface of quartz solve and decrease the active points on the surface of quartz which can adsorb anion collector.     

Elution of lead from vermiculite with environmentally benign reagents

The elution of lead from vermiculite was investigated by using a novel biodegradable chelating reagent,L-asparagic-N,N-diacetic acid(ASDA)and water soluble depolymerized pectic acid and comparing with a conventional chelating reatent,EDTA,as well as acetic acid.The influences of the reagent concentration,equilibrium pH and the suspension contact time on Pb extraction were examined.It is concluded that the acetic acid is not effective for Pb removal in any case due to its weak complexing ability with Pb.Although Pb is easier to be released by EDTA with stoichiometric amount,it is by no means the preferable alternative for the purpose because of its low biodegradability.On he other hand,ASDA and depolymerized pectic acid have the potential application because they are not only effective for Pb elution but also environmentally friendly.     

Optimization and mechanism of gold-bearing sulfide flotation

In order to overcome the difficulty of extracting gold from gold-bearing sulfide ore by cyanide process flotation was adopted based on mineralogical analysis Mineralogy shows that gold particles are of superfine structure and mainly enclosed by sulfide ores. Primary gold-bearing sulfide ore is fine-grained pyrite and arsenopyrite. The paper describes the effects of ratios and dosage of activators and collectors on the recovery and grade of gold concentrate. A proper flotation flowsheet was then proposed based on experimental condition and closedcircuit test. The gold concentrate with the gold grade of25.14 g ton-1and the recovery of 86.94 % is obtained after one rougher, three cleaners, and four scavengers from fine grinding flotation process. Furthermore, the mechanisms of combined activators and combined collectors were studied by thermodynamic calculation, and structure–activity relationship of flotation reagent was also explained     

XPS characteristics of sulfur of bio-oxidized arsenic-bearing gold concentrate and changes of surface nature of bio-oxidation residue

During bio-oxidation of sulfides, the chemical state change of sulfur is a complex and key factor. It is not only an indicator of the extent and intensity of the bio-oxidation, but also controls the property of bio-leaching medium and the period of oxidation. The chemical state of sulfur in sulfides oxidized by leaching bacteria was studied with XPS. Sulfide minerals in the arsenic-bearing gold concentrate consist of pyrite, arsenopyrite, chalcopyrite, galena, sphalerite and so on. In order to probe the pattern of the chemical state change of sulfur in the bio-oxidation residue of arsenic-bearing gold concentrate, the structure of the grains, and the surface nature of the residue, XPS test was carried out through different sputtering duration. The study of XPS clearly shows that: sulfides is progressively oxidized from the surface of minerals to the core by leaching bacteria; the chemical valence of sulfur changes from S^2- or [S2]^2- to [SO4]^2- ; sulfur in the core is in a reduction state, S^2- or [S2]^2- , but exists in an oxidation state S^6 on the surface; due to the chemical state change of sulfur, mineral phase of the bio-oxidation residue is also changed(sulfides inside, while sulfates outside); the layered structure is found in the grains of the bio-oxidation residue.     

Solid-phase extraction gold from alkaline cyanide solution with quaternary ammonium surfactant

The solid-phase extraction(SPE) technique applied to the extraction of organic compound was creatively used as the extraction of inorganic gold in the paper.Two types of techniques were proposed and explored,namely the SPE and the liquid–liquid extraction(LLE) of the quaternary ammonium surfactant [cetytrimethyl ammonium bromide(CTMAB),cetyl pyridine bromide(CPB),benzyl dimethyl dodecyl ammonium chloride(BDMDAC),and dodecyl trimethyl ammonium chloride(DTMAC)].The surfactant could react with Au(CN)_2~-to form the ionic complex,and the compound could be extracted by SPE column of reversed-phase bonded silica gel.Hence,a new method of SPE was proposed to extract gold with these features of the high selectivity,the reliability,and the simplicity.The experimental result shows that the recovery rate of gold is more than 98 %,and the solid-phase extraction column is not easily damaged and it can be repeatedly used.The new method can be used as the extraction process of gold from alkaline cyanide solution as well.Besides,the paper also puts forward a new process of gold extraction.     

Microwave assisted atmospheric acid leaching of nickel from laterite ore

The recovery of nickel from laterite ore with sulphuric acid under the effect of microwave irradiation was studied.The experimental results indicated that the extraction rate of nickel was influenced by reaction time,sulphuric acid concentration,and temperature,especially by microwave power.The results obtained from the experiments of orthogonal arrays showed that the optimum conditions of sulphuric acid concentration,reaction time,microwave power,and temperature were 25 vol.%,1.5 h,600 W,and 90°C,respectively.Under the optimal conditions,the nickel recovery could reach approximately 90.8%,which was higher than that obtained by conventional water bath heating.Kinetic experiments showed that the leaching of nickel in a sulphuric acid medium was controlled by chemical reaction occurring on the surface of laterite ore.The apparent activation energy was 38.9 kJ/mol.Microwave heating technology is efficient,clean,and easy to control and facilitate continuous processing of materials.     

Characterization of Intracellular Gold Nanoparticles Synthesized by Biomass of Aspergillus terreus

Greener synthesis of nanoparticle is a revolutionizing area in research field.Biological method of reduction of metal ions is often preferred because they are clean,safe,biocompatible,and environmentally acceptable than physical,chemical,and mechanical methods.The wet biomass of Aspergillus terreus（A.terreus） was utilized for the intracellular synthesis of gold nanoparticles.Gold nanoparticles were produced when an aqueous solution of chloroauric acid was reduced by A.terreus biomass as the reducing agent.Production of gold nanoparticles was confirmed by the color change of biomass from yellow to pinkish violet.The produced nanoparticles were then characterized by FT-IR,SEM,EDS,and XRD.The SEM images revealed that the nanoparticles were spherical,irregularly shaped with no definite morphology.Average size of the biosynthesized gold nanoparticles was 186 nm.The presence of the gold nanoparticle was confirmed by EDS analysis.Crystalline nature of synthesized gold nanoparticle was confirmed by XRD pattern.     

Kinetics of stripping of gold loaded in DBC organic phase by sodium sulfite

The kinetics of stripping of gold loaded in dibutyl carbito (DBC) organic phase by sodium sulfite was investigated in a Lewis cell. After the stirring speed reached 400 r·min-1, the reaction of gold stripping conformed with the pseudo-first-order reaction. The stripping rate of gold was in direct proportion to interfacial area, concentration of sodium sulfite and reaction temperature. The experimental results showed that the process of stripping gold was controlled by inter-facial chemical reaction, and its activation energy was 36.06 kJ·mol-1. The kinetics equation was put forward for gold stripping by sodium sulfite.     

Electroplating zinc transition layer for electroless nickel plating on AM60 magnesium alloys

Electroplating zinc coating as transition layer of electroless nickel plating on AM60 magnesium alloys was investigated. The zinc film can be deposited in a pyrophosphate bath at 50-60 ℃ under current density of 0.5-1.5 A/dm^2. A new fore treatment technology was applied by acid cleaning with a solution containing molybdate and phosphorous acid, by alkaline cleaning in a bath containing molybdate and sodium hydroxide. The subsequent electroless plating was carried out in nickel sulfate bath. The SEM observation shows that the deposition is uniform and compact. The polarization curve measurements show that the corrosion potential of the zinc plating in 3.5% NaCl is about -1.3 V（vs SCE） which is noble than that of magnesium substrate. The zinc eleetroplating can be applied as the pretreatment process for electroless nickel plating on magnesium alloys.     

A novel flotation scheme: selective flotation of tungsten minerals from calcium minerals using Pb–BHA complexes in Shizhuyuan

The similar floatabilities of calcium minerals and the huge difference between scheelite and wolframite have resulted in difficulties during their separation by flotation in Shizhuyuan Mine. In this study, novel collectors, lead complexes of benzohydroxamic acid(Pb–BHA),were introduced to modify the surface properties of scheelite and wolframite, thereby effectively and selectively improving floatability. The Pb–BHA complexes are found to be selective for the separation of scheelite and calcium minerals with little use of depressants and enable the synchronous flotation of scheelite and wolframite.Hence, a novel flotation process was developed for the recovery of tungsten minerals. The process is simplified greatly, and the recovery is improved by almost 10%.Removing or decreasing the amount of water glass contributes to the improvement of tungsten and fluorite recovery and the circulation of water and reagents, which benefits the environment.     

Preparation and properties of scintillating glass doped with organic activators

A series of scintillating glasses were developed by doping organic activators into low melting temperature glasses according to different ratios. The fluorescence spectra and the transmission spectra of some scintillating glasses were explored and the actual concentration organic in scintillating glass was estimated. The results show that it is feasible to prepare the scintillating glass by doing organic scintillating activators into the low-melting glasses. There are two main reasons for the weak optical properties of the scintillation glasses： one is that the actual concentration of organic activators doped in the glasses is very low, and the other is the existence of lots of defects formed in the scintillating glasses due to the evaporation of organic activator, lowering the transmission of glasses. The fluorescence emission peaks of the glasses move to a longer wavelength compared with those in organic matrixes. To increase the light output of the glass, the optical transmittance of the glasses must be improved and the concentration of activators in the glasses must be increased.     

Novel technology of purification of copper electrolyte

The effects of arsenic with different valence states on the purification of copper electrolyte were studied and a novel technology of purification of copper electrolyte by copper arsenite was proposed. The results show that the purification performance of As（Ⅲ） compounds is better than that of As（Ⅴ） compounds. The purification technology by copper arsenite has the advantages of simple operation, high purification performance and low cost in comparison with other technologies and its appropriate purification conditions are that copper arsenite concentration is 18 g/L, reaction temperature is 65 ℃ and reaction time is 8 h. The removal rates of Sb and Bi are 53.22% and 58.67% respectively under these conditions. The purification principle show that a kind of yellow precipitate mainly composed of arsenic, antimony （ Ⅴ ）, bismuth and oxygen forms in electrolyte after copper arsenite is added, and consequently antimony and bismuth are removed from electrolyte.     

Bioleaching of refractory gold ore （ Ⅲ ）——Fluid leaching Jinya refractory gold concentrate by Thiobacillus ferrooxidans

A novel fluidized-bed reactor was designed and installed for bloleaching in a semi-continuous way, by which a process for biuleaching-cyanidation of Jinya refractory gold arsenical concentrate was studied. The arsenic extraction rate reaches 82.5 % after 4-day batch biooxidation of the concentrate under the optimized condition of pH 2.0, ferric ion concentration 6.Sg/L and pulp concentration 10%. And leached rate of gold in the following cyanida.tion is over 90%. The parameters of three series fluidized-bed reactors exhibit stability during the semi-continuous bioleaching of the concentrate.Armmic in the concentrate can be got rid of 91% after 6-day leaching. Even after 4 days, 82% of arsenic extraction rate was still obtained. The recovery rates of gold are 92 % and 87.5 % respectively in cyaniding the above bioleached residues.The results will provide a base for further commercial production of gold development.     

Recovery of germanium from lignite by microorganism

The recovery of Ge from lignite by microorganism includes tow stages:(1) the breaking-down of Ge complex of humus in lignite into simple compunds assisted by microorganism;(2) the desorption of Ge compounds from the lignite.The recovery rate of Ge has been enhanced by 14% since the discovery of adsorption and desorption of Ge from coal.The effects of pH,leaching agents,and coal size on the recovery of Ge were experimentally investigated,and the optimized process parameters were obtained.The reaction heat of Ge adsorption and desorption in lignite was determined.It is about 23-53kJ/mol,which reveals that the adsorption belongs to physical process,The recovery rate of Ge from lignite with direct microorganism leaching can reach about 85%,Which is higher than that of 60% reported elsewhere.A potential process for leaching Ge in lignite was suggested.     

Influence of Trace Oxygen on the Mechanical Properties of High Pure Silver during Natural Aging

Two kinds of high pure silver materials with 5.3 ppm oxygen and 32.7 ppm oxygen were prepared by various melting processes, both samples were subjected to accumulative rolling with 95% thickness reduction. Their mechanical properties were tested during long natural aging. Results showed that the Ag sheet with 5.3 ppm oxygen is at full annealed state when natural aging 58 days or kept at 150℃ for 30 minutes, and the Ag sheet with 32.7 ppm oxygen is a little of recovery when natural aging a year. It is suggested that appropriate oxygen interstitial solute in Ag solid solution and a few of Ag2O particles at Ag grain boundaries impede the recovery and recrystallization of Ag sheets.