A novel cyclic process using CaSO4/CaS pellets for converting sulfur dioxide to elemental sulfur without generating secondary pollutants: Part II. Hydrogen reduction of calcium-sulfate pellets to calcium sulfide

The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088 K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37.     

A study of the metal sulfide-sulfur dioxide reaction in aqueous media by reaction pressure characterization and ultraviolet spectrophotometry

The metal sulfide-sulfur dioxide reaction has been characterized for seven different sulfide ores by using the changes in sulfur dioxide pressure during the reaction and by ultraviolet spectrophotometric analysis of the reaction products. The UV analysis, which showed that thiosulfuric acid is a major product of the metal sulfide-sulfur dioxide reaction, was used to monitor the r rate of formation of thiosulfuric acid during the reaction. Results from a series of base-line experiments using ferrous sulfide showed a high correlation between the rate of change of sulfur dioxide pressure, the rate of appearance of ferrous ion, and the rate of formation of thiosulfuric acid. These results were compared with those obtained in similar experiments with six naturally-occurring sulfide ores. Finally, the UV method was employed to monitor the kinetics of the decomposition of thiosulfuric acid into elemental sulfur. Using these results, in conjunction with the mechanisms previously developed for the Wackenroder reaction and the acid decomposition of thiosulfate, a mechanism is proposed for the acid oxidative dissolution of sulfide ores which accounts for the formation of elemental sulfur.     

间接碘量法测定稀土硫化物中硫

试验提出了一种用间接碘量法测定稀土硫化物中硫含量的方法:稀土硫化物易与盐酸反应生成硫化氢,而硫化氢气体易和碘反应,故用已知浓度和用量的碘标准溶液完全吸收硫化氢气体,再用已知浓度的硫代硫酸钠标准溶液滴定出未反应的碘标准溶液,从而间接计算出稀土硫化物中硫含量。通过溶剂的选择、碘标准溶液用量及反应摇动时间的研究,确定了适宜的反应条件。结果表明,在稀土硫化物中硫质量分数为10%～25%时的最佳反应条件是:用盐酸作为反应溶剂,0.1 mol/L碘标准溶液用量为35 mL,反应开始至滴定前的剧烈摇动时间为2 min。采用实验方法对稀土硫化物中具有代表性的Ce₂S₃、Sm₂S₃及La₂S₃这3种样品中的硫进行了测定,结果的相对标准偏差(RSD,n=11)小于1%。测定结果与高频红外吸收法及硫酸钡重量法的测定值基本相符。     

加压氧化浸出工艺的机理研究

加压浸出法具有流程短、砷浸出率高、浸出时间短及无SO2等有毒物质产生的优点,是预处理含硫、砷金矿石或金精矿的有效手段.在酸性介质中,硫化物、铁化合物与砷化物发生高温氧化的主要反应包括3种形式:硫化物全部被氧化成硫或硫酸盐,反应过程中产生的Fe2+被氧化成Fe3+,砷被氧化成砷酸盐.随着易处理矿石资源日益减少,加压浸出法...     

Reduction of metals from sulfides

Existing notions on reduction of metals from oxides and sulfides are based on realization of dissociative processes associated with the formation of simple substances. Metal sulfides can be considered as compounds of oppositely charged species formed owing to totality of electrostatic and coordination binding in the Me^z+-S^2? system. Reduction of metals from such compounds with the use of donor properties of sulfide sulfur is an electrochemical process with the participation of the electrode pair Me^z+ and S^2? in the mode of internal electrolysis in the system, which provides utilization of elemental sulfur that is formed through chemical reactions. As an electrochemical medium, molten caustic soda is proposed. In its presence, elemental sulfur disproportionates with the preferential accumulation of sulfide and sulfate sulfur. The reaction causes irreversibility of the reduction process.     

The Future of Copper Metallurgy

Copper technology changed from the vertical to the horizontal furnace and from the roast reaction to the converting reaction towards the end of the last century. However, the horizontal furnace proved to be an inefficient and polluting reactor. As a result many attempts were made to replace it. In the past 40 years new successful melting processes were introduced on an industrial scale that were more energy efficient and less polluting. In addition, smelting and converting were conducted in a single reactor to which the concentrate was fed and the raw copper was produced. The standing problem in many countries, however, is marketing 3 tons of sulfuric acid per ton of copper produced. The new technology offers the option of reducing SO₂, to elemental sulfur by injecting a reducing agent in the gas stream. Another possibility is injecting NH₃, gas to form ammonium sulfate as a co-product. The hydrometallurgical route offers the possibility of obtaining elemental sulfur at moderate temperature and pressure thus solving the sulfur problem.     

锑冶炼中砷碱渣与二氧化硫烟气综合回收清洁工艺探讨

通过将炼锑中产生的含砷碱渣经过浸出、含砷碱溶液吸收废气二氧化硫、硫化钠等硫化剂脱砷、硫酸铁深度除砷以及净化浓缩干燥等过程后,难以处理的砷碱渣和废气低含量的二氧化硫得到彻底处理．整个处理过程,锑回收率达到99％,砷开路率超过90％,二氧化硫吸收率超过95％,使烟气达到排放标准,碱转化为亚硫酸钠,达到了以废治废的目的,是一种清洁炼锑的工艺．     

锑冶炼中砷碱渣与二氧化硫烟气综合回收清洁工艺探讨

通过将炼锑中产生的含砷碱渣经过浸出、含砷碱溶液吸收废气二氧化硫、硫化钠等硫化剂脱砷、硫酸铁深度除砷以及净化浓缩干燥等过程后,难以处理的砷碱渣和废气低含量的二氧化硫得到彻底处理。整个处理过程,锑回收率达到99%,砷开路率超过90%,二氧化硫经吸收超过95%,使气体达到排放标准,碱转化为亚硫酸钠,达到了以废治废的目的,是一种清洁炼锑的工艺。     

碘量-重量法测定脱硫灰还原产物中硫化钙和亚硫酸钙

准确测定硫化钙和亚硫酸钙的含量,对于脱硫灰还原工艺的参数选择和转化进程的研究具有重要意义。用过量碘标准滴定溶液将样品中的硫化钙和亚硫酸钙氧化,磷酸(1+4)溶液溶解样品并调节pH值,硫代硫酸钠标准滴定溶液返滴定得到硫化钙和亚硫酸钙消耗的碘标准滴定溶液的量,从而得到硫化钙和亚硫酸钙的总含量;硫化钙与碘反应生成硫单质,用热氢氧化钾溶液洗脱生成的硫单质的质量得到样品中硫化钙的含量,两者之差即为亚硫酸钙的含量,从而建立了脱硫灰还原产物中硫化钙和亚硫酸钙的测定方法。将实验方法应用于不同工艺流程得到的脱硫灰还原产物测定,7次平行测定硫化钙和亚硫酸钙结果的相对标准偏差(RSD,n=7)为0.54%~1.8%。按照实验方法,对3种配制的脱硫灰还原产物中硫化钙和亚硫酸钙进行测定,测定值均和理论值相符。     

碘量-重量法测定脱硫灰还原产物中硫化钙和亚硫酸钙

准确测定硫化钙和亚硫酸钙的含量,对于脱硫灰还原工艺的参数选择和转化进程的研究具有重要意义。用过量碘标准滴定溶液将样品中的硫化钙和亚硫酸钙氧化,磷酸(1+4)溶液溶解样品并调节pH值,硫代硫酸钠标准滴定溶液返滴定得到硫化钙和亚硫酸钙消耗的碘标准滴定溶液的量,从而得到硫化钙和亚硫酸钙的总含量;硫化钙与碘反应生成硫单质,用热氢氧化钾溶液洗脱生成的硫单质的质量得到样品中硫化钙的含量,两者之差即为亚硫酸钙的含量,从而建立了脱硫灰还原产物中硫化钙和亚硫酸钙的测定方法。将实验方法应用于不同工艺流程得到的脱硫灰还原产物测定,7次平行测定硫化钙和亚硫酸钙结果的相对标准偏差(RSD,n=7)为0.54%~1.8%。按照实验方法,对3种配制的脱硫灰还原产物中硫化钙和亚硫酸钙进行测定,测定值均和理论值相符。     

Reduction of arsenic acid with aqueous sulfur dioxide

The reduction of arsenic acid with aqueous sulfur dioxide in sulfuric acid solutions is presented. First order kinetics with respect to arsenic acid and sulfur dioxide concentrations are observed. Appreciable reduction occurs only when tetravalent sulfur is present as sulfur dioxide. The protonation of arsenic acid in strong sulfuric acid solutions decreases the rate of pentavalent arsenic reduction.     

Combined exposures of human ciliated cells to different concentrations of sulfur dioxide and nitrogen dioxide

In the present study we investigated the influence of two common air pollutants, sulfur dioxide (SO2) and nitrogen dioxide (NO2) on ciliary beat frequency (CBF). Ciliated cells were obtained by nose brush from 12 healthy volunteers and placed on a polycarbonate membrane which was in contact with Ringer's electrolyte solution. This allowed the supply of the cells by capillarity in parallel to the reaction of the pollutants with the cell surfaces. In an exposure chamber the cells were exposed for 30 min. at 37 degrees C either to SO2 (2.5-12.5 ppm) or to NO2 (3.0-15.0 ppm), or to a mixture of NO2 (12.0 ppm) and SO2 (2.5 or 5.0 ppm). CBF was measured by video-interference-microscopy. With SO2 we observed a dose-dependent decrease in CBF with Ringer's solution. 2.5 ppm SO2 caused a 42.8% decrease and 12.5 ppm a decline of approximately 100% (8.10 +/- 0.24 Hz vs. 0.28 +/- 0.20 Hz). In parallel, we observed a decrease in the pH-value from 7.4 to 3.6. 30 min. NO2 exposure (3.0-15.0 ppm) induced a significant dose dependent increase in CBF from 8.4 +/- 0.34 Hz to 9.4 +/- 0.44 Hz. Exposure to a mixture of SO2 and NO2 with Ringer's solution revealed that SO2 exerts a stronger influence on CBF than NO2. Exposure to both pollutants resulted in the same as exposure to SO2 alone. Our findings demonstrate a strong correlation between SO2-modified pH values and CBF. Exposure to a combination of two pollutants revealed the dominant influence of SO2 on CBF while the augmented effect of exposure to NO2 alone might be due to the oxidative potential of this gas.     

A magnetization-chemisorption study of hydrogen and sulfur dioxide on iron

Magnetization-pressure isotherms are measured for hydrogen and sulfur dioxide on small iron particles. The hydrogen isotherms are shown to relate directly to hydrogen uptake and obey the Temkin isotherm. The bonding of hydrogen to iron surfaces at different temperatures is determined from the data and related to other work. This conclusion is that the bond type of hydrogen on iron changes as a function of temperature. The formation of two hydrogen species on iron and at defects in the iron lattice is related to anomolous hydrogen diffusion in iron and to hydrogen embrittlement. The reactions of SO₂ and hydrogen on an iron surface are shown to explain the inhibiting effect SO₂ has an hydrogen embrittlement. Formerly a Graduate Assistant at Syracuse University, is now with the Naval Research Laboratory, Washington     

二氧化锰和硫化锰两矿法制备高纯硫酸锰

利用天然二氧化锰粉与硫化锰精矿为原料制备高纯一水硫酸锰,并取得了初步成功。其最优工艺为：以二氧化锰与硫的摩尔比为2．25：1,在温度90~C条件下浸出3h后,除渣,再用A试剂1．5倍理论用量除去硫酸锰溶液中的钾钠,按工业硫化钡1．5倍理论用量除去各重金属,用氟化锰5倍理论用量除去钙镁后蒸发结晶烘干,得到高纯一水硫酸锰产品。     

A process for the production of magnesium oxide from serpentine by sulfur dioxide leaching and solvent extraction

The applicability of sulfur dioxide leaching for the recovery of magnesium from either natural or calcined serpentine has been investigated. Factors which influence the magnesium recovery such as time, temperature and particle size have been studied, and the optimum values were determined. It has been suggested that the kinetics of the reaction are controlled by diffusion phenomena. The possibility of recovering pure magnesium sulfite from the leach solutions containing iron, nickel, calcium, etc. using the liquid-liquid extraction technique is indicated.     

Left ventricular perimysial collagen fibers uncoil rather than stretch during diastolic filling

Workers in the pulp and paper industry are exposed to different substances, such as hydrogen sulfide and other reduced sulfur compounds, chlorine, chlorine dioxide, sulfur dioxide, terpenes, and paper dust. The exposure level depends on the process, i.e., sulfite, sulfate, groundwood, bleachery, or paper production. Hitherto, exposures have been poorly described and more studies are certainly needed. Workers with repeated exposure peaks to chlorine, e.g., bleachery workers, seem to have an impaired lung function and an increased prevalence of respiratory symptoms. Exposure to high levels of paper dust, (> 5 mg/m3) causes impaired lung function. Therefore, exposure to respiratory irritants is an important, and probably overlooked, occupational risk among certain groups of pulp and paper workers. Some studies indicate that sulfate workers with high exposure to reduced sulfur compounds have an increased mortality due to ischemic heart disease. However, before any definite conclusions can be drawn, the impact of important confounders, such as shift-work and smoking habits have to be further evaluated.     

Transient Inclusion Evolution During Modification of Alumina Inclusions by Calcium in Liquid Steel: Part I. Background,Experimental Techniques and Analysis Methods

In aluminum-killed steels, modification of solid alumina inclusions is often carried out by calcium treatment, converting the alumina to liquid calcium aluminates. When calcium treatment is performed, calcium can either react with sulfur in the melt or with solid alumina. Calcium sulfide inclusions are solid at steel casting temperatures and thus would be detrimental to castability if they remained in the steel after calcium treatment. The aim was to study the transient evolution of inclusions after calcium treatment, testing the hypothesis that calcium sulfide may form as an intermediate reaction product, which can subsequently react with alumina to form modified calcium aluminates. The first part gives the project background and describes the experimental and quantification techniques adopted, including the effect of sampler size in laboratory melts. Results of the formation of intermediate calcium reaction products in laboratory and industrial heats are presented in the second part.     

铬酸钡分光光度法测定高硫铝土矿中硫酸根

硫化物形态的硫含量是铝土矿选矿关注的指标,而其含量常采用总硫减去硫酸根含量的方式计算得出,因此测定高硫铝土矿中硫酸根的方法受到关注。采用盐酸(1+1)分解高硫铝土矿,氨水沉淀法分离铝和铁,碳酸铵沉淀法分离钙,过滤,在酸性溶液中,加入铬酸钡悬浊液与硫酸根生成硫酸钡沉淀和铬酸根离子,用氨水调节pH值至9~10,过滤除去多余的铬酸钡和生成的硫酸钡,滤液即为被硫酸根所置换出的铬酸根溶液,采用铬酸钡分光光度法进行测定,通过铬酸根的吸光度值间接计算出硫酸根的含量,实现了对高硫铝土矿中硫酸根的测定。对显色条件进行了优化,结果表明,硫酸根质量浓度在1~200μg/mL范围内与其对应的吸光度呈线性关系,线性相关系数为0.9999,检出限为0.36μg/mL。将实验方法用于高硫铝土矿实际试样中硫酸根的测定,结果的相对标准偏差(RSD,n=6)为1.6%~1.8%,回收率为95%~105%。分别采用实验方法和重量法对高硫铝土矿中硫酸根进行测定比对,二者结果基本一致。     

Lime-enhanced reduction of sulfide concentrates: A thermodynamic discussion

The need to control or eliminate sulfur dioxide emissions from sulfide smelters has increased the drive to develop new processes for the extraction of metal from sulfide minerals. One such process currently gaining interest is the lime-enhanced reduction of metal sulfides. This paper discusses the thermodynamic aspects relevant to chalcopyrite, chalcocite, and pyrrhotite reduction with hydrogen, carbon monoxide, or carbon in the presence of lime. The effects of temperature and gas composition on sulfide reduction are also discussed. ΔG°vs T diagrams for lime-enhanced sulfide reductions with hydrogen, carbon monoxide, and carbon are constructed and discussed together with some experimental results produced by the authors.     

印度尼西亚海砂氧化性球团氢气还原机理

对印度尼西亚海砂矿氧化性球团氢气还原的规律做了较详细的研究.实验采用失重的方法,通过对反应过程的物相变化、热力学以及动力学方面的分析,探究了海砂球团矿氢气还原的机理.结果表明:温度在800℃和850℃,还原反应的最终产物主要是FeTiO₃,整个反应限制环节是由两个不同阶段的过程组成,反应开始阶段由界面化学反应控制,之后由界面化学反应与内扩散共同控制;在900、950和1000℃三个温度下,反应产物中有钛氧化物出现,整个还原反应由三个不同的限制性环节组成,开始由界面化学反应控制,反应中间阶段是由界面化学反应和内扩散共同控制,反应后期则是由内扩散控制为主.