Investigation of Heavy Metals and Radionuclide’s Impact on Environment Due to The Waste Products of Different Iron Processing Industries in Chittagong, Bangladesh

The waste products, such as induction furnace slag, ladle furnace slag, air pollution control dust, and ramming mass collected from major iron processing industries in Chittagong, Bangladesh were analyzed for heavy metals and naturally radioactive elements. The concentrations of heavy metals Fe, Cr, Mn, Co, Cd, Ni, Pb, Cu and Zn were obtained from atomic absorption spectrophotometer (AAS) analysis with flame atomizer and the radioactivities due to 226Ra, 232Th and 40K were determined using high purity germanium (HPGe) detector of well shielded gamma-ray counting system. From the mean specific activities of the above three natural radionuclides in the investigated samples, the radium equivalent activity (Raeq) and the external hazard index (Hex) were calculated. The study showed the prospect of contamination of environmental materials (viz., soil, water, air, plant) due to many of these investigated elements by using the collected waste products in landfill. The chemical process of ion exchange indicates that the elevated heavy metals in soil can play a role to increase the natural radioactivity of the soil. The obtained Raeq as well as Hex indicated the insignificant radiation hazard due to the activities of primordial radionuclides found in the investigated samples.

Leaching process of germanium oxide dust

A thermodynamic analysis on the acid leaching process of germanium oxide dust and discussion on the behaviors of main substances of the dust in the leaching process were carried out. The effects of temperature, acid concentration, leaching time and stirring speed on the leaching rate of germanium were investigated. Based on the characteristic of the dust, the kinetics and reactive mechanism of acid leaching were studied. The results show that the leaching of the dust by acid belonged to ＂the unreacted core shrinking model＂ of producing solid outgrowth layer. The chemical reaction was controlled by inner diffusion process. The apparent activation energy of leaching process was 12.60 kJ/mol. The leaching reaction of germanium was determined to be mainly second order reaction. The optimum conditions were the reaction temperature of 363 K, the leaching time of 2.5 h, the stirring speed of 120 r/min, the solid-to-liquid ratio of 1/8 and the acid concentration of 120 g/L. Under these conditions, the leaching rate of germanium can come up to more than 87%.

A novel hydrothermal method for zinc extraction and separation from zinc ferrite and electric arc furnace dust

A novel hydrothermal process was developed to extract zinc from pure zinc ferrite（ZnFe2O4） nanopowder and zinc-containing electric arc furnace（EAF） dust using hexahydrated ferric chloride（FeCl3-6H2O） as a decomposing agent.The effects of solid FeCl3-6H2O to ZnFe2O4 ratio by mass（RF/Z）,hydrothermal reaction temperature,and time on zinc extraction were systematically investigated.In the results,when the hydrothermal reaction is conducted at 150℃ for 2 h with RF/Z of 15：20,the efficiency of zinc extraction from ZnFe2O4 reaches97.2%,and the concentration of ferric ions（Fe^3＋） in the leaching solution is nearly zero,indicating a high selectivity for zinc.In addition,the zinc extraction efficiency from the EAF dust reaches 94.5%in the case of the hydrothermal reaction performed at 200℃ for 10 h with the solid FeCl3-6H2O to EAF dust ratio by mass（RF/EAF dust） of 15：10.Zinc and iron separation is achieved by adjusting the pH value of the leaching solution according to the different precipitation pH values of metal hydroxides.

Numerical simulation of the direct reduction of pellets in a rotary hearth furnace for zinc-containing metallurgical dust treatment

A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.

Mechanism research of gas and coal dust explosion

Combined with the experimental results from the large tunnel of the ChongqingResearch Institute,the mechanism of gas and coal dust explosion was studied.Someconcepts about gas and coal dust explosion were introduced such as the form conditionand influential factors.Gas and coal dust explosion propagation was researched and thelifting process of coal dust was simulated.When an explosion occurred due to great mixtureof gas and air,the maximum explosion pressure appeared in the neighborhood of theexplosion source point.Before it propagated to the tunnel of the deposited coal dust,themaximum explosion pressure appeared to be in declining trend.Part of the energy waslost in the process of raising the deposited coal dust through a shock wave,so the maximumexplosion pressure was smallest on the foreside of the deposited coal dust sector.On the deposited coal dust sector,the explosion pressure rapidly increased and droppedoff after achieving the largest peak value.Because of coal dust participation in the explosion,the flame velocity rose rapidly on the deposited coal dust and achieved a basic stablevalue;coal dust was ignited to explode by initial laminar flame,and the laminar flametransformed into turbulent flame.The turbulence transformed the flame fold into a funnelshape and the shock wave interacted with the flame,so the combustion rate rose and thepressure wave was further enhanced.The regeneration mechanism between the flamecombustion rate and the aerodynamic flowing structure achieved the final critical state forforming the detonation.

Basic properties of steel plant dust and technological properties of direct reduction

Basic physicochemical properties of the dust from Laiwu Iron and Steel Co. Ltd. were studied. It is found that C, Zn, K, Na, etc. exist in the fabric filter dust, off gas （OG） sludge, fine ash in converter, and electrical field dust in sinter. Among these, OG sludge gives the finest particle, more than 90% of which is less than 2.51 mm. The dust can lead to a serious negative influence on the production of sintering and blast furnaces （BF） if it is recycled in sintering. The briquette and reduction experimental results showed that the qualified strength could be obtained in the case of 8wt% molasses or 4wt% QT-10 added as binders. Also, more than 75% of metallization ratio, more than 95% of dezincing ratio, as well as more than 80% of K and Na removal rates were achieved for the briquettes kept at 1250℃ for 15 min during the direct reduction process. SEM observation indicated that the rates of indirect reduction and carbonization became dominating when the bri-quettes were kept at 1250℃ for 6 min.

Mathematical simulation of direct reduction process in zinc-bearing pellets

A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.

Simulation of DC glow discharge plasma with free-moving dust particles in the radial direction

A self-consistent fluid model is developed to investigate the radial distributions of dusty plasma parameters in a DC glow discharge,in which the extended fluid approach of plasma particles and the transport equations of dust particles are coupled.The electrical interaction between charged dust particles is considered in the model.The time evolution of radial distributions of dust density,plasma density,the radial component of electric field and the forces acting on dust particles when dust density tends to be stable,are obtained and analyzed under different discharge currents and dust particle radii.It is shown that the dust density structure is determined mainly by the radial electrostatic force,thermophoretic force and ion drag force in the discharge tube,and both discharge current and dust particle radius have an obvious effect on the transport processes of dust particles.The dust particles gather in the central region of the discharge tube for low discharge current and small dust radius,then dust voids are formed and become wider when the discharge current and dust radius increase.The plasma parameters in the dust gathering region are obviously affected by the dust particles due to the charging processes of electrons and ions to the dust surface.

Mathematical model of the direct reduction of dust composite pellets containing zinc and iron

Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.

Application of the Waelz technology on resource recycling of steel mill dust

The Waelz process is the oldest and most often applied technology for the recycling of dusty steel mill residues worldwide,especially for EAF dust.It is a pyro-metallurgical process characterized by the volatilization of non-ferrous metals like zinc,lead and cadmium out of an oxidised solid mixture by means of reduction by coke in a rotary kiln without generating a liquid slag.The recycling of EAF dust closes the material loop between the steel and the zinc industry.Nowadays still more than 50%of the generated EAF dust is lost by sending it to landfill, which means an annual loss of about 800000 t of zinc. The paper gives a short overview about all known recycling techniques for EAF dust before describing in detail the Waelz process.A state-of-the-art Waelz plant fulfils all requirements for environmental protection.It can be operated free of waste water,with low diffuse dust emission and with very low atmospheric emission.The release of heavy metals or dioxin is well controlled by appropriate techniques.At the end of the paper some estimative figures are presented concerning capital expenditure and operating costs.For more precise figures a detailed study is required taking into account the size of the plant and the local conditions.

The Drift of Dust Grains Induced by Transient Magnetic Field

Our experiment shows that the dust grains, suspended on the edge of the sheath of a radio-frequency discharge, undergo a contraction when switching a vertical magnetic field on, and an expansion when switching the magnetic field off. We call this kind of magnetic field "transient magnetic field". A primary analysis is proposed for the phenomenon.

Pyrometallurgical Removal of Arsenic from Electrostatic Precipitators Dusts of Copper Smelting

This work describes the experimental results of pyrometallurgical removing of arsenic from the dust collected in the electrostatic copper precipitators within the gas cleaning system of a Copper Flash Smelting Furnace. The generation of dust in the copper smelting worldwide ranges from 2 - 15 wt% per ton of a copper concentrate. In Chile, copper smelters produce approximately 110 kt/y of dust with a concentration of arsenic between 1 and 15 wt%. The dust is a complex of metals oxides and sulfurs with copper concentrations greater than 10 wt% and relatively high silver concentrations. Since its high arsenic concentration, it is difficult to recover valuable metals through hydrometallurgical processes or by direct recirculation of the dust in a smelting furnace. Thus, the development of pyrometallurgical processes aimed at reducing the concentration of arsenic in the dust (<0.5 wt%) is the main objective of this study, giving particular attention to the production of a suitable material to be recirculated in operations of copper smelting. The work provides a detailed characterization of the dust including the Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN), Scanning Electron Microscope-Energy Dispersive X-ray Analysis (SEM/EDS), X-Ray Diffraction (XRD), the elemental chemical analysis using Atomic Adsorption (AAS), and X-Ray Fluorescence (X-RF). By considering that arsenic volatilization requires a process of sulfidation-decomposition-oxidation, this work seeks to explore the roasting of mixtures of copper concentrate/dust, sulfur/dust, and pyrrhotite/dust. By the elemental chemical analysis of the mixture after and before the roasting process, the degree of arsenic volatilization was determined. The results indicated the effects of parameters such as roasting temperature, gas flow, gas composition, and the ratio of mixtures (concentrate/dust, sulfur/dust, or pyrrhotite/dust) on the volatilization of arsenic. According to the findings, the concentration of arsenic in the roasted Flash Smelting dust can be reduced to a relatively low level (<0.5 wt%), which allows its recirculation into an smelting process.

涂装车间加湿、降温、除尘原理及应用

主要介绍了涂装车间加湿、降温、除尘原理及应用,涂装车间喷漆室、人工操作室体、员工休息区、空调系统均需要用到相关的技术,在策划阶段提前确定各工艺段的温度、湿度、防尘等级,后续设计过程中准确计算和设备选型。

井下巷道喷浆过程产尘的运移及分布特性

煤矿井下全气动喷浆技术的喷射过程涉及浆体基料、喷雾作用与周围空气等,是典型的气、液、固三相流。基于CFD-DPM方法,采用欧拉双流体模型模拟气相和水相,采用拉格朗日模型追踪喷浆过程产生的粉尘,研究了多种工况喷雾作用下粉尘的扩散过程,分析了粉尘运移及分布特性,获得了喷雾角度与流量对粉尘分布的影响规律。喷射角度的变化对粉尘扩散的影响主要集中在中下部区域,控制喷雾流量可有效降低区域粉尘,为合理降尘、提高喷射效率提供了理论支持。

Research on the application of the wet scrubber on the BSSF slag processing system at Baosteel

Based on the analysis results of the dust size distribution of flue gas from Baosteel＇s short-flow （BSSF） slag processing system and the mechanism of the wet scrubber,a wet scrubber system was designed and installed in the No. 1 BSSF slag processing system at Baosteel. The results show that the dust removal efficiency of the previous system that had conventional water nozzles was only 69% with a liquid-gas ratio of 0.79 L/m^3 ,while the dust removal efficiency reached 94% when three sets of high-efficiency dual phase spray guns were installed inside both the flue and the chimney. For the latter system,the liquid-gas ratio was 0. 84 L/m^3 ,and the dust concentration in the cleaned emissions reduced to less than 40 mg/m^3.

Characterization and Pyrometallurgical Removal of Arsenic from Copper Concentrate Roasting Dust

This paper describes the experimental results of removing arsenic from the dust collected in electrostatic precipitators of a fluidized bed roasting furnace (RP dust). The fluidized bed roasting process generates 600 kilotons of copper concentrate per year with 3 - 6 wt% of concentration of arsenic, producing a roasted product with a low content of arsenic below 0.3 wt%. The process generates 27 kilotons of RP dust per year with a concentration of arsenic of the order of 5 wt% and copper concentration of around 20 wt%. Subsequently, the dust collected in the electrostatic precipitators is treated by hydrometallurgical methods allowing the recovery of copper, and the disposition of arsenic as scorodite. This work proposes to use a pyrometallurgy process to the volatilization of arsenic from RP dust. The obtained material can be recirculated in copper smelting furnaces allowing the recovery of valuable metals. The set of experiments carried out in the roasting of the mixture of copper concentrate/RP dust and sulfur/RP dust used different ratios of mixtures, temperatures and roasting times. By different techniques, the characterization of the RP dust determined its size distribution, morphology, and chemical and mineralogical composition. RP dust is a composite material of small particles (<5 μm) in 50 μm agglomerates, mostly amorphous, with a complex chemical composition of sulfoxides. The results of the roasting experiments indicated that for a 75/25 weight ratio of the mixture of the copper concentrate/PR dust under 700℃, 15 minutes of roasting time with injection of air, the volatilization of arsenic reached 96% by weight. The arsenic concentration after the roasting process is less than 0.3% by weight. For a 5/95 mixture of sulfur/RP dust, at 650℃, the volatilization of arsenic reached a promissory result of 67%. Even that this study was carried out for a particular operation, the results have the potential to be extended to dust produced in the roasting of concentrates of nickel, lead-zinc, and gold.

褐煤粉尘对矿区复垦土壤有机碳矿化及细菌群落的影响

煤粉尘沉降至地表后能够显著提高土壤有机碳含量,改变土壤理化性质和土壤微生物群落结构。通过添加褐煤粉尘的土壤培养试验,探究煤粉尘输入的有机碳对土壤有机碳矿化效果及细菌群落的影响。结果表明:在褐煤粉尘影响下,土壤CO_(2)矿化量和矿化速率较对照组最大提升55.02%和54.58%(第5天);土壤易氧化有机碳和土壤微生物生物量碳含量在培养结束后较最大值分别降低40.75和141.39 mg/kg。添加褐煤粉尘导致变形菌门的相对丰度显著降低,而酸杆菌、放线杆菌和厚壁菌门的相对丰度升高。褐煤粉尘输入的有机组分能够在短期内产生激发效应,其自身被土壤细菌分解的过程也能促进土壤CO_(2)的矿化累积,并且提高土壤细菌群落的多样性和变异程度。褐煤粉尘中的有机碳极大程度参与了土壤有机碳库周转过程。

酒钢选矿厂含铁除尘灰资源化利用研究

以酒钢选矿厂含铁除尘灰为研究对象,研究环境除尘灰和烟气除尘灰的选矿技术经济指标,进行除尘灰用于水泥生产物料性质测试,分析用作铁质校正剂的可行性。通过不同应用途径的可行性和经济性分析,为选矿厂合理处置除尘灰提供了依据。

“葵花壳+玉米秸秆”加工粉尘对合作猪养分消化率、小肠组织形态和消化酶活性的影响

试验旨在研究饲粮中添加“葵花壳+玉米秸秆”加工粉尘对合作猪养分消化率、小肠组织形态和消化酶活性的影响。选择平均体重为(9.88±0.82)kg的合作猪50头,进行7 d预试验,饲喂基础饲粮。预试验结束后选取40头平均体重为(11.94±1.43)kg的合作猪,随机分为4组,每组10个重复,每个重复1头猪。对照组饲喂基础饲粮,试验Ⅰ、Ⅱ、Ⅲ组分别饲喂添加5%、10%和15%的“30%葵花壳+70%玉米秸秆”加工粉尘的基础饲粮,正式试验期90 d。结果表明:①试验Ⅱ组粗蛋白和酸性洗涤纤维消化率显著高于对照组(P<0.05);试验Ⅱ、Ⅲ组中性洗涤纤维消化率均显著高于对照组(P<0.05)。②试验Ⅱ组十二指肠绒毛高度显著高于对照组(P<0.05),试验Ⅱ、Ⅲ组空肠绒毛高度显著高于对照组(P<0.05);试验Ⅰ、Ⅱ、Ⅲ组十二指肠隐窝深度极显著低于对照组(P<0.01);试验Ⅰ、Ⅲ组十二指肠绒隐比显著高于对照组(P<0.05),试验Ⅱ组十二指肠绒隐比极显著高于对照组(P<0.01);空肠隐窝深度和绒隐比差异不显著(P>0.05)。③试验Ⅱ、Ⅲ组十二指肠内蛋白酶活性极显著高于对照组(P<0.01),试验Ⅱ组空肠内蛋白酶活性显著高于对照组(P<0.05);试验Ⅱ组试验猪十二指肠内淀粉酶活性显著高于对照组(P<0.05),试验Ⅰ、Ⅱ、Ⅲ组空肠内淀粉酶活性极显著高于对照组(P<0.01)。综上可知,饲粮中添加“葵花壳+玉米秸秆”加工粉尘,可提高合作猪的养分消化率、十二指肠和空肠内蛋白酶和淀粉酶活性,能够改善小肠组织形态,添加水平以10%最佳。

火法冶金工艺处理钢铁厂含铁含锌除尘灰的技术发展现状

钢铁冶炼过程中产生的含铁含锌除尘灰不仅数量庞大且成分复杂,其富含的锌元素对高炉的正常运行及寿命构成威胁,因此无法直接循环使用于原料系统。然而,这些除尘灰中蕴含的铁、锌、铅等金属元素却具有极高的回收利用价值。因此,如何实现含铁含锌除尘灰的高效资源化利用,已成为钢铁企业亟待解决的关键问题,选择适宜的处置方式显得尤为重要。深入探讨了火法冶金技术处理此类除尘灰的原理,并详细列举了当前钢铁企业应用火法冶金处理含锌除尘灰的工艺流程、发展态势以及各自的优缺点。同时,分析了火法冶金工艺处理含铁含锌除尘灰的挑战及对策,旨在为钢铁企业制定科学的除尘灰处置策略及选择最合适的处理工艺提供参考。