Kinetic process of oxidative leaching of chalcopyrite under low oxygen pressure and low temperature

Kinetic process of oxidative leaching of chalcopyrite in chloride acid hydroxide medium under oxygen pressure and low temperature was investigated. The effect on leaching rate of chalcopyrite caused by these factors such as ore granularity, vitriol concentration, sodium chloride concentration, oxygen pressure and temperature was discussed. The results show that the leaching rate of chalcopyrite increases with decreasing the ore granularity. At the early stage of oxidative reaction, the copper leaching rate increases with increasing the oxygen pressure and dosage of vitriol concentration, while oxygen pressure affects leaching less at the later stage. At low temperature, the earlier oxidative leaching process of chalcopyrite is controlled by chemical reactions while the later one by diffusion. The chalcopyrite oxidative leaching rate has close relation with ion concentration in the leaching solution. The higher ion concentration is propitious for chalcopyrite leaching.     

KINETICS OF GOLD LEACHING FROM SULFIDE GOLD CONCENTRATES WITH THIOSULFATE SOLUTION

The reaction process for leaching gold from sulfide gold concentrates containing copperwith ammonia-ammonium thiosulfate solution containing copper(Ⅱ)can be divided into initialstage and later stage of reaction.Initial stage of reaction is controlled by interface reaction.Lat-er stage of reaction is controlled by diffusion process of reaction through solid products layer.Whole leaching process is under the control of corrosion reaction of pyrite bearing gold.Actionof ammonium sulfate in the system is probably as follows:(1)NH_4~ and NH_3 forms a buffer so-lution;(2)SO_4~(2-)ion inhibites the oxidation and decomposition of S_2O_3~(2-)ion.Cu~(2 )ion in thesystem acts as an oxidant and oxygen makes the Cu~(2-)regenerate.     

Effect of tempering temperature on microstructure and mechanical properties of high boron white cast iron

The effect of different tempering temperatures on the microstructure and mechanical properties of airquenched high boron white cast iron was studied.The results indicate that the high boron white cast iron comprises dendritic matrix and inter-dendritic M 2 B boride;and the matrix comprises martensite and pearlite.After quenching in the air,the matrix is changed into lath martensite;but only 1-μm-size second phase exists in the matrix.After tempering,another second phase of several tens of nanometers is found in the matrix,and the size and quantity increase with an increase in tempering temperature.The two kinds of second precipitation phase with different sizes in the matrix have the same chemical formula,but their forming stages are different.The precipitation phase with larger size forms during the austenitizing process,while the precipitation phase with smaller size forms during the tempering process.When tempered at different temperatures after quenching,the hardness decreases with an increase in the tempering temperature,but it increases a little at 450 ℃ due to the precipitation strengthening effect of the second phase,and it decreases greatly due to the martensite decomposition above 450 ℃.The impact toughness increases a little when tempered below 300 ℃,but it then decreases continuously owing to the increase in size and quantity of the secondary precipitate above 300 ℃.Considered comprehensively,the optimum tempering temperature is suggested at 300 ℃ to obtain a good combination of hardness and toughness.     

Bioleaching of low grade nickel sulfide mineral in column reactor

Jinchuan low grade nickel （0.4%-0.6% Ni, mass fraction） sulfide mineral ore contains a remarkably high content of magnesia （30%-35% MgO, mass fraction） present in the main gangue minerals. Bioleaching was performed to investigate the feasibility to process the mineral due to its relative simplicity, eco-friendly operation and low capital cost requirements. The mixed mesophiles were enriched from acid mine drainage samples collected from several acid mines in China. Considering that the magnesia is easily extracted by acid solution and the excessive Mg^2＋ will exceed the tolerance of the mixed mesophiles, three effective means were used to reduce the disadvantage of magnesia during the bioleaching operation. They were adaptation of the mixed mesophiles to improve the tolerance; pre-leaching to remove most leachable magnesia and periodic bleeds of a portion of the pregnant leaching solution to control the level of Mg^2＋ based on the tolerance of the mixed mesophiles. An extraction of nickel （90.3%） and cobalt （88.6%） was successfully achieved within a 300 d leaching process from the Jinchuan low grade nickel sulfide mineral ore using a column reactor at ambient temperature.     

Relationship between the Local Vibration Mode Characteristics and the Charge State of Carbon Acceptor in GaAs

The local vibration mode(LVM)of carbon acceptor in GaAs is studied by measuring directly the changein LVM absorption with a NIC-170 SX FT-IR spectrometer.The change in the charge state of carbon acceptorand the temperature dependence of the LVM absorption were investigated also.The contents of the impuritiesother than carbon were estimated by secondary ion mass spectrometry.It is observed that the frequency,thespectral form and the integrated absorption of the LVM are not affected by the change in charge state of car-bon acceptor.     

Influence of oxygen gas content on the structural and optical properties of ZnO thin films deposited by RF magnetron sputtering at room temperature

Zinc oxide (ZnO) thin films were deposited on sapphire (0001) substrates at room temperature by radiofrequency (RF) magnetron sputtering at oxygen gas contents of 0%,25%,50% and 75%,respectively.The influence of oxygen gas content on the structural and optical properties of ZnO thin films was studied by a surface profile measuring system,X-ray diffraction analysis,atomic force microscopy,and UV spectrophotometry.It is found that the size of ZnO crystalline grains increases first and then decreases with the increase of oxygen gas content,and the maximum grain size locates at the 25% oxygen gas content.The crystalline quality and average optical transmittance (>90%) in the visible-light region of the ZnO film prepared at an oxygen gas content of 25% are better than those of ZnO films at the other contents.The obtained results can be attributed to the resputtering by energetic oxygen anions in the growing process.     

Accelerating column leaching trial on copper sulfide ore

The main measures to accelerate leaching sulfide ore are large spraying intensity,manual oxygen supply,temperature control,and acclimated bacteria.The indoor experiment accelerating sulfide ore leaching detected the temperature during leaching process,dissolvability of oxygen,bacterial concentration,Cu concentration and slag grade.At the same time,this paper also analyzed the effect of four factors,which are bacterial diversity cultivation stage,spraying intensity,air supply,and whether to control temperature,on the leaching efficiency of copper.The results indicate that the oxygen content of leach solution has a close relationship with temperature but it is rarely affected by air supply.The bacterial concentration preserves from 106 to 107 mL^-1,and temperature has a great effect on the bacterial activity under the condition of proper temperature and oxygen supply,and the lack of nutrition prevents the bacterial concentration from rising in the late stage.The relationships of the copper leaching efficiency to temperature,air feed,and spraying intensity are directly proportional.The leaching efficiencies of the cultivated bacteria and acclimation bacteria are 1.2 and 1.4 times as large as that of the original bacteria.     

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%.     

Kinetic study on pressure leaching of high iron sphalerite concentrate

The kinetics of pressure leaching high iron sphalerite concentrate was studied.The effects of agitation rate,temperature, oxygen partial pressure,initial acid concentration,particle size,iron content in the concentrate and concentration of Fe2 added into the solution on the leaching rate of zinc were examined.The experiment results indicate that if the agitation rate is greater than 600 r/min,its influence on Zn leaching rate is not substantial.A suitable rise in temperature can facilitate the leaching reaction,and the temperature should be controlled at 140-150℃.The increase trend of Zn leaching rate becomes slow when pressure is greater than 1.2 MPa,so the pressure is controlled at 1.2-1.4 MPa.Under the conditions of this study,Zn leaching rate decreases with a rise in the initial sulfuric acid concentration;and Zn leaching rate increases with a rise of iron content in the concentrate and Fe 2 concentration in the solution.Moreover,the experiment demonstrates that the leaching process follows the surface chemical reaction control kinetic law of“shrinking of unreacted core”.The activation energy for pressure leaching high iron sphalerite concentrate is calculated,and a mathematical model for this pressure leaching is obtained.The model is promising to guide the practical operation of pressure leaching high iron sphalerite concentrate.     

Sulphidization flotation for recovery of lead and zinc from oxide-sulfide ores

A new flowsheet was developed to recover the valuable minerals from oxide or oxide-sulfide ores of lead and zinc. The flowsheet consisted of flotation of sulfide minerals, desliming and sulphidization-flotation of oxide minerals. The corresponding reagent system and techniques to the flowsheet were investigated. Batch and continuous tests show that the dosage of sodium sulfide, temperature, and collector type are main affecting factors on the recovery of smithsonite and cerussite. For the flotation of cerussite, there is an appropriate dosage of sodium sulfide at which the recovery reaches its maximum value. The required sodium sulfide for smithsonite flotation is higher than that for cerussite and the recovery of smithsonite flotation increases with the dosage of sodium sulfide at low level and becomes insensitive at high dosage. The appropriate temperature for smithsonite and cerussite flotation is found to be 25 ～ 40℃. Amines are found to be the effective collectors for the flotation of smithsonite after sulphidization. Investigation also shows that desliming prior to sulphidization-flotation is essential to the effective recovery of smithsonite and cerussite, and the desliming process of two-stage hydrocyclon is well feasible and effective for the treatment of lead-zinc oxide ores. A further treatment on the cerussite flotation concentrate by shaking table is proposed to obtain higher lead grade.     

含硫油品储罐腐蚀产物硫化亚铁自燃性的研究

模拟油品储罐中硫化亚铁的生成方式，研究了H2S气体在没有氧气存在的条件下与油品储罐内壁腐蚀产物-Fe(OH)3、Fe2O3和Fe3O4发生反应及反应产物硫化亚铁的自燃性.结果表明：油品储罐中腐蚀产物Fe(OH)3、Fe2O3和Fe3O4与H2S在无氧条件下均可发生放热反应生成硫化亚铁，且生成的硫化亚铁与空气接触会发生氧化反应放出热量，热量聚集使油品温度上升是引起油品自燃并导致油品储罐发生火灾和爆炸事故的主要原因.但不同生成方式所生成的硫化亚铁的氧化速度不同，其自燃性也不同.     

有色金属硫化矿中伴生金银资源回收研究进展

有色金属矿产资源中伴生的金银矿物是贵金属金银资源的重要来源,伴生金银的回收一直是各国选矿工作者研究的重点。伴生金银资源主要分布在硫化铜、硫化铜铁及硫化铅锌矿石中,由于共伴生金银嵌布粒度粗细不均,金银捕收剂对矿石的适应能力不强,导致现有浮选工艺及药剂制度难以满足伴生金银回收的要求,严重影响了伴生金银的回收效果。在伴生金银工艺矿物学研究基础上,针对不同矿石中伴生金银资源的回收特点,选矿工作者通过改进和强化磨矿工艺、选择合理的工艺流程及开发多种新型金银捕收剂,显著提高了有色金属硫化矿中伴生金银资源的选矿指标。     

Roasting reaction of ferrous sulfide

The rate and mechanism of oxidation of ferrous sulfide have been studied by means of the spring balance and X-ray diffraction analysis over the temperature range from 500° to 700°C. The complete oxidation to oxides begins at 600°C. At the initial stage of oxidation, a slight increase of weight was found. It was observed by X-ray that the deficiency of iron ion in FeS occurs in this stage. This is interpreted as follows: iron ion reacts with oxygen by migrating from the interior of FeS crystal to the surface, without evolution of SO₂, until the deficiency of iron attains to a limiting value. Above 600°C the rate of oxidation does not change with temperature, so the rate-determining factor is diffusion of gas. Since the observed rate of oxidation depends upon the amount of the sample, the diffusion in the bed of the sample may determine the rate.     

Catalytic effect of activated carbon on bioleaching of low-grade primary copper sulfide ores

The catalytic effect of activated carbon on the bioleaching of low-grade primary copper sulfide ores using mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was investigated. The results show that the addition of activated carbon can greatly accelerate the rate and efficiency of copper dissolution from low-grade primary copper sulfide ores. The solution with the concentration of 3.0 g/L activated carbon is most beneficial to the dissolution of copper. The resting time of the mixture of activated carbon and ores has an impact on the bioleaching of low-grade primary copper sulfide ores. The 2 d resting time is most favorable to the dissolution of copper. The enhanced dissolution rate and efficiency of copper can be attributed to the galvanic interaction between activated carbon and chalcopyrite. The addition of activated carbon obviously depresses the dissolution of iron and the bacterial oxidation of ferrous ions in solution. The lower redox potentials are more favorable to the copper dissolution than the higher potentials for low-grade primary copper sulfide ores in the presence of activated carbon.     

Characterizing gold in refractory sulfide gold ores and residues

Gold is present in refractory sulfide gold ores mainly in arsenian pyrite and arsenopyrite, where it occurs in both the chemically bonded state and as nano-size grains of metallic gold. During roasting or pressure oxidation, the sulfide matrix is destroyed and essentially all the gold is converted to the metallic form. The liberated gold is readily dissolved in conventional cyanide media, although a few residual gold particles, commonly encapsulated by films of silica-rich gel or by calcium sulfate, are detected. Chloridecontaining gold ores can generate soluble gold chlorocomplexes during hydrometallurgical processing and the dissolved gold can be sequestered on the surfaces of associated carbon particles, resulting in reduced gold recoveries.     

Simulation and application of a HVOF process for MCrAIY thermal spraying

This work deals with numerical simulation and application of a high velocity oxygen fuel (HVOF) process for MCrAlY thermal spraying. The main objective of this study was to observe the correlations between coating oxidation and oxygen content in combustion products or flame temperature. Spray parameters were selected on the basis of the numerical simulation of combustion and particle behavior in the flame. The results of experiments revealed that the oxygen content is not the main key factor concerning the oxidation rate of MCrAlY coatings. On the contrary, the flame temperature has a decisive influence on oxidation. Combustion conditions corresponding to stoichiometric factors between 0.82 and 1.2 appeared not to be favorable for MCrAlY thermal spraying. Outside this range, it appeared preferable to use a combustion system on the fuel-rich side.     

Comparative study on simultaneous removal of calcium and sulfate ions from flotation recycling water by aluminum hydroxide

Due to the environmental policies and economic reasons, the water used in some flotation operations of complex sulfide ores is recirculated, causing the ion concentration of some species to increase over time, affecting the flotation of the minerals of interest. In this work, an experimental and thermodynamic analysis of the synthetic solutions was presented with a high content of calcium and sulfate ions. The study focused on evaluating the use of two aluminum compounds for the precipitation of Ca²⁺ and SO₄^2? in the form of ettringite. The amorphous aluminum hydroxide was found to be more efficient than the crystalline one, giving rise to 83% calcium and 91% sulfate removal. The XRD analysis of the solids showed the main reaction product of ettringite, accompanied by small amounts of calcite, due to the absorption of atmospheric carbon dioxide. The final solution after the chemical treatment showed residual calcium and sulfate concentrations below 200 mg/L. Finally, the kinetics of calcium removal appeared to correspond to a second order reaction with respect to calcium concentration, with an apparent activation energy of 53.48 kJ/mol, which may suggest that the ettringite precipitation process is governed by the chemical reaction.     

硫化亚铁在原油储运过程中的危害及防治措施

阐明了原油储罐中硫化亚铁主要来源于硫化氢等腐蚀性气体直接与金属作用,产生的腐蚀产物及硫化氢与铁锈的反应产物。硫化亚铁最主要的危害是其自燃引起火灾,呼吸阀外腔内的硫化亚铁危害最大。分析了原油储罐中硫化亚铁的自燃过程,提出了硫化亚铁自燃事故的预防措施。     

Effect of Oxygen Content on the Oxidation of Pure Iron

The oxidation of pure iron with various oxygen contents was studied. Pure iron and ferrite containing different amounts of oxygen were oxidized for 1–5 hr in two types of oxidation atmospheres at 850°C. Pure iron (0.0037% oxygen) oxidized more rapidly than ferrite (0.017% oxygen). Oxidation is higher in the moist ambient atmosphere than in dry air. The oxidation rate was not proportional to the amount of oxygen in the samples.     

水在金属硫化矿体自燃中的作用

金属硫化矿物氧化起因于硫化矿石固液相界面的电化学反应。水是硫化矿石自热、自燃的关键。注水、石灰水及其他阻化剂的阻燃方法忽视了水溶液中游离氧在硫化矿物氧化过程中所起的巨大作用，因而收效甚微。注水对自燃的矿石有一定的物理降温作用，但对未燃矿石则了电化学升温作用，对深部矿体则起了预热预氧化作用。水的电化学升温助燃作用大于水的降温阻燃作用。