Pretreatment and thiosulfate leaching of refractory gold-bearing arsenosulfide concentrates

A hydrometallurgical process for refractory gold-bearing arsenosulfide concentrates at ambient temperature and pressure was presented, including fine grinding with intensified alkali-leaching （FGIAL）, enhanced agitation alkali-leaching （EAAL）, thiosulfate leaching and displacement. Experimental results on a refractory gold concentrate showed that the total consumption of NaOH in alkaline leaching is only 41% of those theoretically calculated under the conditions of full oxidization for the same amount of arse- nides and sulfides transformed into arsenates and sulfates, and 72.3% of gold is synchro-dissoluted by thiosulfate self-generated during alkaline leaching. After alkaline leaching, thiosulfate leaching was carried out for 24 h. The dissolution of gold is increased to 91.9% from 4.6% by cyanide without the pretreatment. The displacement of gold by zinc powder in the solution gets to 99.2%. Due to an amount of thiosulfate self-generated during alkaline leaching, the reagent addition in thiosulfate leaching afterwards is lower than the normal.

Consolidation mechanism of gold concentrates containing sulfur and carbon during oxygen-enriched air roasting

Consolidation in calcines is a common problem in the oxygen-enriched air roasting of refractory gold concentrates containing sulfur and carbon when the initial temperature is greater than 600?C. To determine the phases that caused consolidation,gold concentrates were roasted under different conditions and the calcines were mainly detected by X-ray diffraction(XRD). The possible underlying mechanism was then studied through comparisons of the XRD patterns of different calcines. The results indicated that the generation of calcium magnesium silicate,iron-doped calcium aluminosilicate,and calcium aluminate caused the consolidation. Furthermore,an enriched oxygen atmosphere accelerated the oxidation reaction and the emitted heat increased the local temperature in calcines. The local temperature was inferred to have increased to the generation temperature zone of the corresponding liquid phases. Oxidation of the pyrite and decomposition of the dolomite and muscovite mainly occurred at the initial stage of oxygen-enriched air roasting. Calcium was confirmed to be essential to the consolidation process.

A new extraction process of refractory gold arsenosulfide concentrates

A new hydrometallurgical process for the refractory gold arsenosulfideconcentrates under normal temperature and pressure was presented. The experimental results of arefractory gold concentrate show that the total consumption of NaOH in alkaline leaching is only 40%of those theoretically calculated under the conditions of full oxidization at the same oxidation ofarsenic to ar-senate and sulfur to sulfate. After alkaline leaching, cyanidation and adsorptionwere carried out for 24 h. The dissolution of gold by NaCN is increased to 95.3% from 12.8% beforepretreatment, and meanwhile 99.3% of the adsorption of gold by activated charcoal. The consumptionof NaCN for one ton ore is 10 kg, which is 1.2 times less than that before pretreatment. As it iscarried out under normal temperature and pressure, the investment of installations is alsodecreased.

Thermal Decomposition of Pyrite, Arsenopyrite and Auriferous Concentrates in the Presence of Sodium

The thermal decomposition of pyrite, arsenopyrite and auriferous concentrates in the presence of sodium hydroxide was studied by using TG DTA and XRD methods. For the arsenopyrite mineral the reaction takes place at 200～350℃ with the formation of Na 2SO 4, Na 3AsO 4, FeSO 4, Fe 8As 10 O 23 and FeAs, and a large amount of FeAsS do not decompose at this temperature. When the temperature arrives at 800℃, the exothermic reaction takes place with the formation of Na 3AsO 4, Na 2SO 4, Fe 2O 3 and a little amount of As 4S 3. For the pyrite mineral the reaction takes place between 200～350℃ with the formation of Fe 2(SO 4) 3, Fe 3S 4, FeS, Na 2Fe(SO 4) 2 in addition to unreacted FeS 2 and NaOH. When the temperature arrives at 800℃, almost all the pyrite decomposes and the Fe 2O 3, Na 2SO 4, Fe(SO 4) 3 and a minor amount of Fe 1- x S are produced. The decomposition temperatures of arsenopyrite and pyrite get lower as their particle sizes are small. The results also indicated that with the addition of an appropriate amount of NaOH, nearly complete containment of arsenic and sulphur during the decomposition of auriferous concentrate may be possible.

Analysis of Raw Materials Components of Dry Composite Mixes for Production Food Concentrates

Background:The simplest and most convenient food technology is the using of dry composite mixtures.They have a lot of advantages.Dry composite mixtures,which would completely be the basis for the production of personalized food concentrates,are not represented.The development of such dry composite mixtures is actual and of scientific and practical interest.The purpose of this research is the selection and justification of local import-substituting raw materials components for dry composite mixtures used as the basis for the production of food concentrates.As the objects of research,the raw materials components of the starch,fruit and vegetable,industry were selected.The work uses currently accepted standard research methods for organoleptic and physic-chemical parameters of raw materials components.The research was carried out within of the project“Theoretical Substantiation of Production Technology and the Development of Import-Substituting Food Products of Functional Purpose Based on Dry Composite Mixtures”,funded by the Belarusian Republican Foundation for Basic Research.Based on the researches,it was found out that in the composition of dry composite mixtures for the production of food concentrates it is expedient to use the following raw materials:potato starch,extruded corn starch,dried carrots,dried beets,dried topinambur and dried apples in chopped form.

Argentinean Copper Concentrates: Structural Aspects and Thermal Behaviour

In Argentina, there are many sources of copper concentrates. Some of them are currently in operation, while others are in the exploration stage. All copper concentrates produced are exported to other countries for copper refinement and to create various finished products. It is desirable that in the near future, these copper concentrates be processed in an Argentinean industrial plant. The aim of this paper was to present the results of a characterisation study carried out on five different copper concentrate samples. The thermal decomposition of the copper concentrates was determined by differential thermal analysis and thermogravimetry (DTA TG). The information was correlated with the chemical composition and the mineralogical phases of the samples identified by X-ray diffraction. A melting test at temperatures of up to 1300℃ was performed to complete the study of the concentrate’s behaviour during heating. After the test, all of the samples were observed by light and electronic scanning microscopy to identify the different phases generated under high-temperature conditions.

Selective leaching of vanadium from V-Ti magnetite concentrates by pellet calcification roasting-H_(2)SO_(4) leaching process

A novel method of pellet calcification roasting-H_(2)SO_(4) leaching was proposed to efficiently separate and extract vanadium(V)from vanadium-titanium(V-Ti)magnetite concentrates.The leaching rate of V is as high as 88.98%,while the leaching rate of impurity iron is only 1.79%.Moreover,the leached pellets can be used as raw materials for blast furnace ironmaking after secondary roasting.X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy with energy dispersive X-ray spectrometry(SEMEDS)analyses showed that V^(3+)was oxidized to V^(5+)after roasting at 1200℃,and V^(5+)was then leached by H_(2)SO_(4).X-ray diffraction(XRD)analyses and single factor experiment revealed a minimal amount of dissolved Fe_(2)O_(3) during H_(2)SO_(4) leaching.Therefore,a high separation degree of V and iron(Fe)from V-Ti magnetite concentrate was achieved through H_(2)SO_(4) leaching.Compared with the traditional roastingleaching process,this process can achieve a high selectivity of V and Fe,and has excellent prospects for industrial production.

CAUSTIC DECOMPOSITION OF SCHEELITE AND SCHEELITE－WOLFRAMITE CONCENTRATES THROUGH MECHANICAL ACTIVATION

Based on physicochemical study of the reaction between scheelite and NaOH, a new decomposition process for scheelite and scheelitewolframite concentrate, i. e., mechenically activating caustic decomposition has been developed, and it has been successfu

Dielectric Characterization and Microwave Roasting of Molybdenite Concentrates at 915 MHz Frequency

The magnetic hysteresis loop was measured to know the magnetic property of molybdenite concentrate.In order to evaluate its microwave absorption capacity, the dielectric properties of molybdenite concentrate was investigated using cavity perturbation method at 915 MHz dependent on densities and temperatures.The parameter data were fitted using regression fit and a model related to the same density and temperature ranges was developed.A nonlinear surface fitting was used to present visually the effect of dielectric parameters on the microwave penetrate depth of molybdnite concentrate.The crystal products of MoO 3 obtained from microwave roasting at different temperatures were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).The results show both the dielectric constants and loss factors increase in the increase of apparent densities and temperatures with different growth rates in the experimental range.Due to the distinguished trend of dielectric performance dependent on temperatures, two parts in the heating scenario for the molybdenite concentrate samples were divided.The microwave penetration depth is inversely proportional to both apparent densities and temperatures.The nonlinear fitting surfaces indicate the increase of dielectric loss provides an enough decrease in microwave penetration depth.In contrast, the dielectric constant has a positive effect for it.Pure MoO 3 was produced at 800 ℃ by using microwave energy.This work can be helpful to design and simulate microwave system for efficient beneficiation of molybdenite concentrate and to prepare molybdenum products from this concentrate.

Efficient ozonation of reverse osmosis concentrates from petroleum refinery wastewater using composite metal oxideloaded alumina

Novel Mn–Fe–Mg-and Mn–Fe–Ce-loaded alumina（Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3） were developed to catalytically ozonate reverse osmosis concentrates generated from petroleum refinery wastewaters（PRW-ROC）. Highly dispersed 100–300-nm deposits of composite multivalent metal oxides of Mn（Mn^2＋）, Mn^3＋,and Mn^4＋, Fe（Fe^2＋）and Fe^3＋ and Mg（Mg^2＋）, or Ce（Ce^4＋） were achieved on Al2O3 supports. The developed Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3 exhibited higher catalytic activity during the ozonation of PRW-ROC than Mn–Fe/Al2O3, Mn/Al2O-3, Fe/Al2O3, and Al2O3. Chemical oxygen demand removal by Mn–Fe–Mg/Al2O3-or Mn–Fe–Ce/Al2O3-catalyzed ozonation increased by 23.9% and23.2%, respectively, in comparison with single ozonation.Mn–Fe–Mg/Al2O3 and Mn–Fe–Ce/Al2O3 notably promoted áOH generation and áOH-mediated oxidation. This study demonstrated the potential use of composite metal oxide-loaded Al2O3 in advanced treatment of bio-recalcitrant wastewaters.

Influence of Ferric and Ferrous Iron on Chemical and Bacterial Leaching of Copper Flotation Concentrates

The effects of ferrous and ferric iron as well as redox potential on copper and iron extraction from the copper flotation concentrate of Sarcheshmeh, Kerman, Iran, were evaluated using shake flask leaching examinations. Experiments were carried out in the presence and absence of a mixed culture of moderately thermophile microorganisms at 50?C. Chemical leaching experiments were performed in the absence and presence of 0.15 M iron (ferric added medium, ferrous added medium and a mixture medium regulated at 420 mV, Pt. vs. Ag/AgCl). In addition, bioleaching experiments were carried out in the presence and absence of 0.1 M iron (ferric and ferrous added mediua) at pulp density 10% (w/v), inoculated bacteria 20% (v/v), initial pH 1.6, nutrient medium Norris and yeast extract addition 0.02% (w/w). Abiotic leaching tests showed that the addition of iron at low solution redox potentials significantly increased the rate and extent of copper dissolution but when ferric iron was added, despite a higher initial rate of copper dissolution, leaching process stopped. Addition of both ferrous and ferric iron to the bioleaching medium levelled off the copper extraction and had an inhibitory effect which decreased the final redox potential. The monitoring of ferrous iron, ferric iron and copper extraction in leach solutions gave helpful results to understand the behaviour of iron cations during chemical and bacterial leaching processes.

A Fuzzy Logic Model to Predict the Bioleaching Efficiency of Copper Concentrates in Stirred Tank Reactors

Multiplicity of the chemical, biological, electrochemical and operational variables and nonlinear behavior of metal extraction in bioleaching environments complicate the mathematical modeling of these systems. This research was done to predict copper and iron recovery from a copper flotation concentrate in a stirred tank bioreactor using a fuzzy logic model. Experiments were carried out in the presence of a mixed culture of mesophilic bacteria at 35° C, and a mixed culture of moderately thermophilic bacteria at 50° C. Input variables were method of operation (bioleaching or electrobioleaching), the type of bacteria and time (day), while the recoveries of copper and iron were the outputs. A relationship was developed between stated inputs and the outputs by means of “if-then” rules. The resulting fuzzy model showed a satisfactory prediction of the copper and iron extraction and had a good correlation of experimental data with R-squared more than 0.97. The results of this study suggested that fuzzy logic provided a powerful and reliable tool for predicting the nonlinear and time variant bioleaching processes.

Mineralogical properties and co-sintering characteristics of fluxed iron ore with magnetite concentrates

To investigate the feasibility of co-sintering of fluxed iron ore with magnetite concentrates, the mineralogical properties of a novel fluxed iron ore were studied using particle size analysis, microscopic morphology characterization, and X-ray diffraction Rietveld analysis. Following that, the experiments for granulation performance and basic sintering characteristics were designed under seven different fluxed iron ore ratios, and the integrated ranking of different fluxed iron ore ratios was determined using gray relation analysis. Finally, the results of the industrial trails were combined with the feasibility analysis. Test and experimental results show that the fraction of the fluxed iron ore particles larger than 0.5 mm can account for more than 48%, and the particles have two morphologies: spherical-rough and flaky-smooth. Ca elements are found in the form of calcite (CaCO3) and dolomite (CaMg(CO3)2). The average particle size of granules and powder removal rate can be improved from 2.50 to 3.16 mm and 39.60% to 24.20%, respectively, with the increase in the fluxed iron ore ratio. Furthermore, the fluxed iron ore can improve assimilability and liquid fluidity of magnetite concentrates. In terms of overall granulation performance and sintering characteristics, the fluxed iron ore ratios are graded from best to worst as follows: 12%, 15%, 9%, 18%, 21%, 6% and 3%. The industrial trails show that when the fluxed iron ore ratio is increased, the beneficial effect of the superior sintering characteristics of the fluxed iron ore itself is ideally balanced with the negative effect of the lower amount of additional CaO at 12% ratio, and thus, it is feasible to bring the fluxed iron ore into production at a level of roughly 12%.

Does progress in microfracture techniques necessarily translate into clinical effectiveness?

BACKGROUND Multitudinous advancements have been made to the traditional microfracture(MFx)technique,which have involved delivery of various acellular 2nd generation MFx and cellular MFx-III components to the area of cartilage defect.The relative benefits and pitfalls of these diverse modifications of MFx technique are still not widely understood.AIM To comparatively analyze the functional,radiological,and histological outcomes,and complications of various generations of MFx available for the treatment of cartilage defects.METHODS A systematic review was performed using PubMed,EMBASE,Web of Science,Cochrane,and Scopus.Patients of any age and sex with cartilage defects undergoing any form of MFx were considered for analysis.We included only randomized controlled trials(RCTs)reporting functional,radiological,histological outcomes or complications of various generations of MFx for the management of cartilage defects.Network meta-analysis(NMA)was conducted in Stata and Cochrane’s Confidence in NMA approach was utilized for appraisal of evidence.RESULTS Forty-four RCTs were included in the analysis with patients of mean age of 39.40(±9.46)years.Upon comparing the results of the other generations with MFX-I as a constant comparator,we noted a trend towards better pain control and functional outcome(KOOS,IKDC,and Cincinnati scores)at the end of 1-,2-,and 5-year time points with MFx-III,although the differences were not statistically significant(P>0.05).We also noted statistically significant Magnetic resonance observation of cartilage repair tissue score in the higher generations of microfracture(weighted mean difference:17.44,95%confidence interval:0.72,34.16,P=0.025;without significant heterogeneity)at 1 year.However,the difference was not maintained at 2 years.There was a trend towards better defect filling on MRI with the second and third generation MFx,although the difference was not statistically significant(P>0.05).CONCLUSION The higher generations of traditional MFx technique utilizing acellular and cellular components to augment its potential in the management of cartilage defects has shown only marginal improvement in the clinical and radiological outcomes.

Recovery of titanium and vanadium from titanium–vanadium slag obtained by direct reduction of titanomagnetite concentrates

A process of NaOH molten salt roasting-water leaching to treat titanium-vanadium slag obtained by direct reduction of titanomagnetite concentrates was investigated.X-ray diffraction(XRD), scanning electron microscopy(SEM) equipped with energy dispersive spectroscopy(EDS), and thermogravimetry-differential scanning calorimetry(TG-DSC) techniques were used to characterize the samples. The results show that anosovite(Mg_(x)Ti_(3-x)O_(5))and clinopyroxene [Ca(Ti,MgAl)(SiAl)_(2)O_(6)] are the major phases of titanium-vanadium slag. In the NaOH molten salt roasting process, titanium is converted to intermediate product Na_(2)TiO_(3) and vanadium is converted to water-soluble vanadate. The response surface methodology(RSM) was used to optimize the roasting process conditions. NaOH to slag mass ratio(N/S) and roasting temperature are the main influential factors. Under the optimal roasting conditions,i.e., roasting temperature of 550℃, N/S of 1.20, and roasting time of 80 min, the conversions of titanium and vanadium are 96.5 % and 93.0 %, respectively. In the water leaching process, Na_(2)TiO_(3) is converted to amorphous structure of H_(2)TiO_(3) since Na^(+)is exchanged with H^(+). Up to 93.0 % vanadium is leached out under the optimal leaching conditions. Titanium and vanadium in the titanium-vanadium slag can be separated and then recovered.

New process for treating boron-bearing iron ore by flash reduction coupled with magnetic separation

Boron is an important industrial raw material often sourced from minerals containing different compounds that cocrystallize,which makes it difficult to separate the mineral phases through conventional beneficiation.This study proposed a new treatment called flash reduction-melting separation(FRMS)for boron-bearing iron concentrates.In this method,the concentrates were first flash-reduced at the temperature under which the particles melt,and the slag and the reduced iron phases disengaged at the particle scale.Good reduc-tion and melting effects were achieved above 1550℃.The B_(2)O_(3) content in the separated slag was over 18wt%,and the B content in the iron was less than 0.03wt%.The proposed FRMS method was tested to investigate the effects of factors such as ore particle size and tem-perature on the reduction and melting steps with and without pre-reducing the raw concentrate.The mineral phase transformation and morphology evolution in the ore particles during FRMS were also comprehensively analyzed.