Oxidative Leaching Research Articles

The effect of carbon black on the oxidative leaching of enargite by manganese(IV) dioxide in sulfuric acid media

• Since MnO 2 is nobler than enargite, they form a galvanic corrosion couple causing strong interaction between them.

Geoinformation Modeling of Sulfide Frost Weathering in the Area of Udokan Deposit

The developed geoinformation technology based on the experimental and computer-aided physicochemical modeling enables quantitative calculation and mapping of aftereffects of geochemical processes in sulfide material dumps in terms of Udokan copper deposit. The role of nitrogen as a component of acid rains is emphasized together with its effect on chemical weathering of sulfides. The authors report modeling and testing data on oxidative leaching of Udokan sulfide ore using nitrogen compounds. The classical and geoinformation approaches to calculating leakage flux being of importance for exploration and geoecology studies in permafrost are compared. The obtained results on intensification of sulfide oxidation under conditions of permafrost allow estimating potential environmental impact of the planned mining operations at Udokan deposit and can be used to improve the current cryo-geotechnologies of metal ore mining.

Uranium comminution age tested by the eolian deposits on the Chinese Loess Plateau

The U234/238U ratio of fine particles can record the time since their separation from bed rock because of the disruption of uranium series equilibrium introduced by the recoil of daughter 234Th nuclei (precursor of 234U) out of particle surfaces during the decay of 238U. Application of the uranium comminution age method, which has great potential in tracing production and transportation of sediments is however complicated by the weathering dissolution of U234 depleted particle surfaces, the difficulty in determining the fraction of recoiled nuclei, and the precipitation of exogenetic U234. Here we minimize these complications by using a newly developed precise size separation using electroformed sieve, and a chemical protocol that involves reductive and oxidative leaching. Eolian deposits collected from the Chinese Loess Plateau (CLP) were used to test the validity of our method. Possible effects of weathering dissolution were also evaluated by comparing samples with different weathering intensities. The results show decreasing 234U/238U ratios in fine eolian particles with increasing sedimentation age, agreeing well with the theoretical prediction of the comminution age model. This successful application of the uranium comminution age approach to the eolian deposits on the CLP is also aided by a stable dust source, the low weathering intensity, the lack of consolidation, and the well-defined age model of the deposits. A transportation time of 242±18 ka was calculated for the eolian deposits, which indicates a long residence time, and thus extensive mixing, of the dust particles in source regions, partly explaining the stable and homogeneous composition of the eolian dust over glacial–interglacial cycles.

φ–pH diagram of As–N–Na–H2O system for arsenic removal during alkaline pressure oxidation leaching of lead anode slime

In order to illustrate the thermodynamic characteristics of arsenic during alkaline pressure oxidation leaching process of lead anode slime (NaNO3 as oxidant; NaOH as alkaline reagent), the φ–pH diagrams of As–Na–H2O, N–H2O, As–N–Na–H2O systems at ionic mass concentration of 0.1 mol/kg and temperatures of 298, 373, 423 and 473 K were established according to thermodynamic calculation. The results show that the existence forms of arsenic are associated with pH value, which mainly exists in the forms of H3AsO4, H2AsO4−, HAsO42−, and As2O3 in lower pH region, while it mainly exists in the form of when pH>11.14. High alkali concentration and high temperature are advantageous to the arsenic leaching. The alkaline pressure oxidation leaching experiments display that the tendency of arsenic leaching rate confirms the thermodynamic analysis results obtained from the φ–pH diagrams of As–N–Na–H2O system, and the highest leaching rate of arsenic reaches 95.85% at 453 K.

Improvements in gold ore cyanidation by pre-oxidation with hydrogen peroxide

It is known that the presence of sulphidic minerals in the cyanidation of gold ores may cause significant consumption of oxygen supplied in the injected air. This may result in dissolved oxygen starvation for the oxidative leaching of the gold, and ultimately it will reduce the maximum attainable recovery of gold from the ore. In addition, the presence of sulphides leads to extra consumption of the cyanide-leaching agent, NaCN, due to the formation of thiocyanate, therefore increasing costs. These types of gold sulphidic ores may be pre-treated prior to cyanidation by means of an oxidation step, converting the sulphides into oxides or sulphates. This treatment leads to a reduction in the consumption of dissolved oxygen and of cyanide in the cyanidation step and to an improvement in the metallurgical recovery. In the current work we present the results of a five month full-scale trial carried out in a gold extraction plant in Brazil, which normally operated with three tanks in series carrying out an alkaline pre-oxidation step using compressed air only, followed by a train of fourteen aerated and mechanically-agitated tanks for the cyanidation. The ore feeding the leaching circuit averages 1.70gAu/t, with about 2.5% of pyrrhotite (FeS) as the main sulphide constituent. The addition of 60L/h of concentrated hydrogen peroxide, H2O2, 50%w/w (density=1.19g/mL) for pre-oxidation of a slurry of 60% solids at a rate of 150t/h (dry ore) resulted in a marked increase in dissolved oxygen (DO). This addition corresponds to a dosing rate of 0.24kg 100%H2O2 per ton of dry ore and increased the dissolved oxygen level from an average of about 1.0 to 7.2mg/L in the pre-oxidation tanks. It also led to an overall reduction of NaCN consumption from an average of 0.52 to 0.40kg/t of ore, and an increase in metallurgical Au recovery from an average of 91.3% to 92.5%.

Study on the Oxidative Leaching of Uranium from the Lignite in the CO32-/HCO3- System

Na2CO3/NaHCO3 mixtures with different oxidants were used to leach uranium in the lignite which was obtained from Lincang, Yunnan province. The experimental results showed that the optimal solid/liquid ratio and CO32-/HCO3- ratio for uranium leaching were 1 : 20 (g/mL) and 2 : 1, respectively. With the increase of carbon concentration from 0.1 mol/L to 1.1 mol/L, the leaching efficiency of uranium increased from 14.64% to 42.39% after 6 h leaching. The oxidants could significantly enhance the uranium leaching efficiency, which was up to 72.23% by injecting O2 at 1.5 L/min after 12 h leaching. The oxidative leaching process of uranium from the lignite was better fitted to the pseudo-second-order reaction model. The sequential extraction results illustrated that the oxidants could effectively enhance the leaching of organic matter bound uranium in the lignite, which was decreased from 76.86 mg/kg to 9.00 mg/kg by injecting O2. The infrared spectrum analysis demonstrated that the corresponding transmittance at about 3197 cm−1 was prominently reduced after the oxidative leaching, which intimated that the phenolic and alcoholic hydroxyl might be the main functional groups combined with uranium in the lignite.

Development of a Combined Flotation and High Pressure Leaching Process for Copper and Nickel Recovery from Mine Tailing

The present study focused on the re-processing of copper and nickel from mine tailings. In this work, recovery of copper and nickel from mine tailing by combined process of flotation and high pressure oxidative leaching were considered. In the first stage, effects of flotation parameters including collector type, collector dosage, and pH and pulp density were examined. The results showed that over 80% copper recovery was achieved under the optimized flotation conditions while nickel recovery was lower than 30% due to its co-ex-istence with gangue minerals of pyrrhotite, pyrite and other clay minerals. In the second stage, key parameters, particularly concentration of sulfuric acid, temperature, pressure and leaching time were investigated to test the leaching efficiency of copper and nickel from the flotation concentrate with high pressure oxidative leaching (HPOL). A comparison was made between the leaching efficiencies of copper and nickel from flotation concentrates and mine tailing.

Copper Recovery from Silicate-Containing Low-Grade Copper Ore Using Flotation Followed by High-Pressure Oxidative Leaching

Copper Recovery from Silicate-Containing Low-Grade Copper Ore Using Flotation Followed by High-Pressure Oxidative Leaching

Selective extraction of gold (III) from hydrochloric acid–chlorine gas leach solutions of copper anode slime by tri-butyl phosphate (TBP)

The oxidative leaching causes to dissolve various impurities such as Fe, Cu, Pd, Se in copper anode slime. Organic extractant tri-butyl phosphate (TBP) was used to purify leach solution. Several parameters, such as TBP, HCl and chloride inorganic salt concentrations were chosen in order to determine efficient state for impurities separation. Standard solvent extraction tests for extraction and separation of Au, Pd, Pt, Fe, Cu and Se were conducted with equal volume of aqueous and organic phases in batch experiments. The effect of hydrochloric acid, organic phase and metals initial concentration were examined at ambient temperature. It was found that 0.25 mol/L TBP in the presence of 2.5 mol/L hydrochloric acid can cause high extraction of gold. Meanwhile, in these conditions the extraction of other impurities is negligible. After extraction, pregnant organic phase was scrubbed by distilled water and some impurities were removed. Finally, gold was stripped by sodium thiosulfate solution. The stripping solution does not have any impurities. By adding H2SO4 to stripping solution containing Na2S2O2, SO2 gas is released and Au3+ ions could be reduced.

Pretreatment of tin anode slime using alkaline pressure oxidative leaching

Abstract The pretreatment of tin anode slime using alkaline pressure oxidative leaching was studied. The effects of different parameters on the extractions of various metals were investigated based on thermodynamic calculation. The results indicated that the optimum leaching conditions were 2.5 M of NaOH concentration, 130 °C of temperature, 1.5 h of time, 1 MPa of oxygen partial pressure, 7 mL/g of liquid-to-solid ratio and 700 rpm of stirring speed. Under the conditions, the extractions of tin and arsenic reached 92.16% and 96.49% respectively, but that of copper and lead were at a low level. Meanwhile, antimony, bismuth, and silver were hardly dissolved into the NaOH solution. The leachate was then subjected to an evaporation and cooling crystallization process for arsenic removal. After the purification, 94.36% of arsenic was separate from the lixivium as sodium arsenate hydrate and the final solution can be used to produce sodium stannate.

Green Recovery of Rare Earths from Waste Cathode Ray Tube Phosphors: Oxidative Leaching and Kinetic Aspects

In this work, we developed a green and efficient process for the recovery of rare earths from waste cathode ray tube phosphors. The mixture of hydrochloric acid and hydrogen peroxide was identified as the most suitable leaching agent due to the synergistic effect. The effects of various parameters on leaching process were explored, and the optimal conditions with stirring speed 600 rpm, temperature 313 K, 1 M of H2O2, 4 M of HCl, and leaching time of 90 min were determined. Furthermore, a possible reaction mechanism was proposed, and the kinetics for the leaching process was investigated in detail. The leaching process was found to follow a shirking-core model, with the chemical reaction as the rate-controlling step. The apparent activation energy of the reaction was calculated as 52.3 kJ/mol, and the reaction orders for H2O2 and HCl were established as 0.82 and 2.13, respectively. The kinetic equation was established. Moreover, the optimal leaching conditions were applied to the waste phosphors, and the ...

Selective and Efficient Extraction of Zinc from Mixed Sulfide–oxide Zinc and Lead Ore

ABSTRACTMixed sulfide–oxide lead and zinc ores are generally composed of both sulfides and oxides. The dissolution of sulfides is more difficult than oxides thus the addition of oxidant is necessary. In this paper, oxidative leaching of mixed ore in NH3-(NH4)2SO4 solution using ammonium persulfate as oxidant under atmospheric pressure and relatively low temperature was investigated for the first time. The effects of factors on the leaching of pure ZnS were studied and the optimal conditions with zinc 98.7% were determined. Selective and efficient extractions of 93.9% and 94.9% zinc from zinc sulfide ore and mixed ore were also achieved, respectively.

Acid leaching decarbonization and following pressure oxidation of carbonic refractory gold ore

Carbonate decomposition of carbonic refractory gold ore and the following pressure oxidation were studied. In the carbonate decomposition procedure, the effects of liquid-to-solid ratio and reaction time on decomposition ratio of carbonate were investigated. The experimental result shows that the decomposition ratio of carbonate is 98.24% under the conditions of liquid-to-solid ratio of 5:1, Fe3+ concentration of 20 g/L, sulfuric acid concentration of 20 g/L, reaction temperature of 80 °C and reaction time of 2 h. Then, the slurry obtained from carbonate decomposition was put into the titanium autoclave for pressure oxidation leaching. Effects of liquid-to-solid ratio, temperature, time and oxygen partial pressure on sulfur oxidation ratio were studied during pressure oxidation. With the prolonged time, pyrite and arsenopyrite are oxidized to ferric subsulfate, hydrated ferric sulfate and jarosite, resulting in the increasing residue ratio. The residue ratio and the sulfur content in the residue can be decreased by ferric subsulfate dissolution. The oxidation ratio of the sulfur is 99.35% under the conditions of oxidation time of 4 h, temperature of 210 °C, oxygen partial pressure of 0.8 MPa and stirring speed of 600 r/min.

Kinetics of Uranium Extraction from Uranium Tailings by Oxidative Leaching

Extraction of uranium from uranium tailings by oxidative leaching with hydrogen peroxide (H2O2) was studied. The effects of various extraction factors were investigated to optimize the dissolution conditions, as well as to determine the leaching kinetic parameters. The behavior of H2O2 in the leaching process was determined through scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) and x-ray diffraction analysis of leaching residues. Results suggest that H2O2 can significantly improve uranium extraction by decomposing the complex gangue structures in uranium tailings and by enhancing the reaction rate between uranium phases and the leaching agent. The extraction kinetics expression was changed from 1 − 3(1 − α)2/3 + 2(1 − α) = K 0(H2SO4)−0.14903(S/L)−1.80435(R o)0.20023 e −1670.93/T t (t ≥ 5) to 1 − 3(1 − α)2/3 + 2(1 − α) = K 0(H2SO4)0.01382(S/L)−1.83275(R o)0.25763 e −1654.59/T t (t ≥ 5) by the addition of H2O2 in the leaching process. The use of H2O2 in uranium leaching may help in extracting uranium more efficiently and rapidly from low-uranium-containing ores or tailings.

Recovery of Mo and Ni from spent acrylonitrile catalysts using an oxidation leaching–chemical precipitation technique

An oxalic acid (H2C2O4) and hydrogen peroxide (H2O2) leaching–chemical precipitation process was developed to recover valuable metals from the spent acrylonitrile catalysts that primarily contain Mo, Ni, Fe and Bi. H2C2O4 and H2O2 leaching studies indicated good leaching efficiencies for Mo and very low efficiencies for Ni because of the formation of soluble molybdenum oxalate complexes and a nickel oxalate (NiC2O4) precipitate, which was separated by filtration. Under the optimal leaching conditions (H2C2O4 concentration of 1.25mol/L, H2O2 concentration of 0.20mol/L, leaching temperature of 50°C, liquid-to-solid (L/S) ratio of 20mL/g and leaching time of 2.5h), 99.7% of Mo was dissolved into the liquid phase, and 98.4% of Ni remained in the residues. For purification, the molybdenum oxalate complexes in the leaching liquor were broken down by adding the emulsion of Ca(OH)2 to form calcium molybdate (CaMoO4) and calcium oxalate (CaC2O4) precipitates; molybdenum trioxide (MoO3) was then recycled, followed by processes of acid dissolution, ammonium molybdate deposition, and calcining. The NiC2O4 in the leaching residues was dissolved and converted into soluble nickel-oxalate-ammonium complexes by adding ammonium hydroxide (NH4OH), and pure NiC2O4 powders were obtained from the filtered liquor through an ammonia stilling process after filtration. In this case, 95% of the Mo and 97% of the Ni in the spent catalyst were recovered as MoO3 and NiC2O4 with purities of 97.88% and 99.91%, respectively. Based on the results of the present study, a tentative process flow sheet is proposed.

Combined oxidative leaching and electrowinning process for mercury recovery from spent fluorescent lamps

In this paper, oxidative leaching and electrowinnig processes were performed to recovery of mercury from spent tubular fluorescent lamps. Hypochlorite was found to be effectively used for the leaching of mercury to the solution. Mercury could be leached with an efficiency of 96% using 0.5M/0.2M NaOCl/NaCl reagents at 50°C and pH 7.5 for 2-h. Electrowinning process was conducted on the filtered leaching solutions and over the 81% of mercury was recovered at the graphite electrode using citric acid as a reducing agent. The optimal process conditions were observed as a 6A current intensity, 30g/L of reducing agent concentration, 120min. electrolysis time and pH of 7 at the room temperature. It was found that current intensity and citric acid amount had positive effect for mercury reduction. Recovery of mercury in its elemental form was confirmed by SEM/EDX. Oxidative leaching with NaOCl/NaCl reagent was followed by electrowinning process can be effectively used for the recovery of mercury from spent fluorescent lamps.

Oxidative leaching behavior of metalliferous black shale in acidic solution using persulfate as oxidant

The oxidative dissolution of metalliferous black shale in sulfuric acid solution using sodium persulfate as an oxidant was investigated. The effects of leaching factors including leaching temperature, leaching time, stirring speed, initial concentration of sodium persulfate and sulfuric acid and particle size on the leaching rate were studied as well. The leaching kinetics of molybdenum, nickel and iron from metalliferous black shale shows that the leaching rate is controlled by a chemical reaction through a layer on the unreacted shrinking core. The leaching process follows the kinetics model 1–(1–a)1/3=kt with apparent activation energies of 34.50, 43.14 and 71.79 kJ/mol for Mo, Ni and Fe, respectively. The reaction orders in sodium persulfate are 0.80, 1.01 and 0.75 for molybdenum, nickel and iron, respectively, while in sulfuric acid, these orders are 0.45, 0.75 and 0.50 for molybdenum, nickel and iron, respectively. In addition, the reaction mechanism for the dissolution of the metalliferous black shale was discussed.

Effect of selected parameters on stibnite concentrates leaching by ozone

A novel leaching process for stibnite concentrates using ozone as oxidant has been studied in this paper. The main factors affecting the leaching rate such as leaching temperature, concentration of leaching agent, gas flow rate and liquid to solid ratio have been investigated comprehensively. In addition, the effect of ferric chloride and sodium chloride on antimony extraction has been studied. The results indicate that the leaching efficiency (%) of the antimony increases with the increase of those factors mentioned above. And the form that the antimony dissolves into solution is SbCln3−n, while the sulfur mainly retains in the residue in the form of sulfur element. The oxidation leaching of stibnite concentrates has achieved antimony recoveries in excess of 99% under the optimum experimental conditions after 5h of leaching.

Study of the dissolution of chalcopyrite in solutions of different ammonium salts

41BC6=D= The oxidative leaching of chalcopyrite in ammoniacal solutions has been evaluated using electro-analytical techniques and controlled bulk leaching studies. The anodic dissolution process has been established to be a sevenelectron transfer process under nitrogen in ammonia–ammonium sulphate solutions and ammonia–ammonium carbonate solutions, which suggests that the sulphur is oxidized to thiosulphate and the copper and iron released as Cu + and Fe2+ in these systems. The deportment of Fe2+ and S 2O3 2- is affected by choice of the ammonium salt used in the leaching process. In the perchlorate salt, only five electrons are transferred, supporting formation of different sulphur species as proposed for the sulphate and carbonate salts. Scanning electron microscopy and energydispersive spectroscopic analysis of the mineral surface after leaching indicate presence of an iron–sulphur surface layer completely free of copper in the sulphate system, an iron-rich surface layer in the perchlorate solutions, and absence of surface layer build-up in carbonate solutions. XRD analysis of a bulk leach residue from leaching in ammoniaammonium sulphate solutions showed the surface layer to be mostly amorphous (90%). The crystalline content (10%) is composed of 95% polymorphs of anhydrous iron oxide hydroxide FeO(OH). Choice of ammonium salt and the hydrodynamic environment of leaching have been shown to influence the presence or absence of the surface product, as well as its nature. HF1�C@9= chalcopyrite, ammonia, surface deposits, coulometry, iron oxy-hydroxide.

Gangue minerals reactivity in oxidative leaching of uraninite with dilute sulfuric acid from low-grade ores: an approach for better leach liquor purity

This paper presents results of sulfuric acid leaching studies carried out on a low-grade uranium ore with emphasis on attaining maximum uranium leachability with minimum content of detrimental ions like Si, Al, Fe, Mg and P, which originate from reactive gangue minerals like chlorite, biotite and apatite. A “two-stage leaching” scheme was developed wherein the total reaction time and the pH of the slurry were split such that the initial phase consists of higher acidity with shorter reaction period and the later phase involves reduced acidity and longer reaction time. This modification gives leach liquor of higher purity with good uranium leachability at relatively lower acid consumption.