利用熔融分步还原法优化铜渣贫化效果及渣型结构

根据铜渣中物相成分及熔池熔炼过程工艺特点,对高温条件下熔融铜渣还原过程热力学以及实验过程进行了研究。传统的铜渣一步还原金属回收法,产物中往往得到大量金属合金,降低了熔渣中金属回收率,为避免还原程度控制不当生成金属合金,本实验采用分步还原法分别对铜渣中的有价金属铜、铁进行回收,分析了熔池温度、助熔剂CaO和还原剂炭粉添加量对渣还原贫化过程中贫化效果的影响,掌握了还原过程中渣结构的类型转变。结果表明,温度1350℃,沉降时间40min,熔渣中CaO控制量为22%(质量分数,下同),还原剂炭粉添加量为2.29%时,渣中Cu_2O的还原率达到95.36%,而还原剂炭粉量控制为8%时,渣中铁相沉降率和金属化率分别达到83.13%和85.30%。此时,由于贫化条件的适当控制,避免了铜铁金属混合物的还原析出,实现了渣中铜铁相的深度贫化,促进了铜熔渣贫化效果。此外,铜渣还原贫化过程中,由于助熔剂CaO和还原剂炭粉的添加,熔渣中铁氧化物被控制进行逐步还原,促使渣型由结构复杂的SiO_2-Fe_3O_4-FeO高粘度渣系逐步转变为结构简单、低粘度、低熔点的CaO-Al_2O_3-SiO_2三元渣系,体系渣型得到了有效优化,为后续铜渣的资源化利用提供了性能稳定的渣型。     

氟磷酸钙真空碳热还原反应机理

在真空条件下,本文采用热力学分析、XRD及化学分析等方法与手段,对SiO2在氟磷酸钙碳热还原制磷的过程进行了研究,考察了SiO2的添加量对磷矿还原率的影响.通过热力学研究,在压力100Pa温度低于1075℃ 时,Ca5(PO4)3F与C、SiO2的反应满足反应发生的热力学条件.实验研究表明:在真空度10Pa～80Pa,温度达到实验最高温度1550℃时,二氧化硅不能使氟磷酸钙发生脱氟反应,与热力学计算结果一致.还原率随着温度升高而增大,在低于1450℃时,添加SiO2有利于提高还原率;随m增加,还原率也增加,在1350℃时,还原率增大速度较快.由此作者提出了SiO2对氟磷酸钙真空碳热还原的反应机理.     

SiO2对氟磷酸钙真空碳热还原反应的影响

采用热力学分析、X射线衍射及化学分析等手段,对真空下SiO2在氟磷酸钙碳热还原过程的行为以及siO2添加量对还原率的影响进行了研究.热力学结果表明,当压力为100 Pa和温度高于1075℃时,Ca5(PO4)3F与C、SiO2的反应满足反应发生的热力学条件.实验研究表明:在系统压力10～ 80 Pa,温度达到实验最高温度1550℃,siO2不能使氟磷酸钙发生脱氟反应,与热力学计算结果吻合.还原率随着温度升高而增大,低温下,添加SiO2有利于氟磷酸钙碳热还原反应;当硅钙摩尔比SiO2／CaO从0.3增至1,还原率随之增加.     

钒渣组成对V_2O_3溶解能力的影响

利用高温淬火方法得到钒渣渣系的高温物相,采用X-ray衍射分析方法确定钒渣的物相组成,分别研究了V2O3含量及n(FeO)/n(SiO2)对钒渣中V2O3溶解能力的影响。结果表明,钒铁尖晶石和Fe3O4为钒渣中存在的固定相;钒渣中V2O3含量不断增加,V2O3的溶解度随之增加,但n(FeO)/n(SiO2)1.5,V2O3增加到一定量时,溶解度无明显变化;n(FeO)/n(SiO2)不断增大,V2O3在钒渣中的极限溶解度也随之增加。     

对真空条件下氧化锌制备锌的机理及冷凝的研究

本文对锌资源概况、制锌工业的现状与发展等方面进行了综述,对氧化锌真空碳热还原过程分别采用热力学、沸点、蒸气压计算进行分析。热力学计算结果显示,碳的热还原氧化锌反应的理论起始温度随着压强的减小而减小,由常压减小到10Pa时,起始温度由原来的1247K减小到473K;CO气体还原氧化锌反应常压下的理论起始反应温度为1198K,当压力降到10Pa时,起始温度降为404K,由沸点分析可知,分离比Zn高的沸点元素Pb、In、Al、Cu、Sn、Fe在热力学上是可行的;由饱和蒸汽压分析可知,粗锌中各组元的蒸馏顺序分别为:CdZnPbInSnAlCuFe。真空下,可以防止冷凝过程中二氧化碳与锌发生再氧化反应。由此,本文提出了采用真空炉的方法从氧化锌中制取锌的工艺。     

红土镍矿真空碳热还原过程中硅的挥发行为

为了解红土镍矿在真空碳热还原过程中SiO2的还原特性和还原过程的主要影响因素,在系统压力2～200 Pa下,以分析纯的SiO2、Fe2O3以及煤炭为原料,在热力学分析的基础上,采用X射线衍射、扫描电子显微镜-能量散射谱和化学成分分析等手段,研究了Fe/Si摩尔比、配碳量对SiO2还原过程、硅的挥发率和还原反应速率的影响。通过热力学计算,得出Fe,Si氧化物被碳还原的化学反应自由能和还原反应临界温度,表明在100 Pa条件下SiO2的临界反应温度降低了477～584 K。实验结果表明:Fe/Si摩尔比的增大和配碳量的增加,均降低了Si的挥发率,提高了SiO2还原反应速率;SiO2发生了气化反应生成了SiO气体并在石墨冷凝系统歧化生成Si和SiO2,且有部分SiO气体与石墨或者CO反应生成SiC;反应残渣中的石英颗粒被Fe-Si合金和SiC包围,结合紧密。     

SiO2在真空低价氟化法炼铝过程的分布

热力学研究得出:当系统残余压力为100~10 Pa时,SiO2与碳反应在1465~1353 K以上即可生成Si和CO;在1329~1225 K以上即可生成SiC和CO;SiO2和还原剂碳及氟化铝在1464~1353 K以上反应生成SiF4和CO及铝。实验考察了真空低价氟化法炼铝过程中SiO2的分布。XRD表明:SiO2在低价氟化法炼铝过程中有五种走向:(1)被还原成SiC,存在于残渣相;(2)被还原为单质硅,再与还原出的铁生成硅铁,存在于残渣相;(3)SiO2与冰晶石生成铝硅酸盐进入气相中;(4)SiO2与冰晶石生成气态SiF4,再与冰晶石分解的氟化钠形成Na2SiF6进入冷凝相;(5)形成气态低价氧化硅,再在合适温度下分解为单质硅进入冷凝相。     

CaC_2还原MgO热力学分析与实验研究

本文对常压及真空条件下以碳化钙为还原剂制取金属镁的热力学分析,计算出平衡状态下镁蒸汽的露点,并进行真空热还原实验研究.结果表明:常压下临界反应温度为2095K;当系统压力降至10~3Pa和10Pa,临界反应温度依次降为1376K和1030K;达到平衡时,还原温度1316K时,镁蒸汽的露点为熔点,还原温度为1273K、1373K时,露点分别为901K、958K.升高还原温度或延长还原时间可提高镁收率和CaC_2利用率;理论配比的反应物料在1423K条件下还原2h的镁收率为83.1%.而当还原时间达到2.5h,镁还原率和CaC_2利用率均超过80%.     

碳酸钙/铜渣复合固硫剂热解性能分析研究

首次分析研究铜渣作为添加剂,加入到碳酸钙中形成的碳酸钙/铜渣复合固硫剂的热解性能。通过XRD、DTA、BET、SEM分析可知,铜渣的加入能够改善碳酸钙/铜渣复合固硫剂的热解性能。热解分析表明:铜渣中的铁橄榄石(Fe2SiO4)、磁铁矿(Fe3O4)、白云石(CaMg(CO3)2)在高温下热解,产生对烟气脱硫有积极作用的Fe2O3、CaO、MgO、SiO2等物质。当铜渣加入量为10%(质量分数)时,碳酸钙/铜渣复合固硫剂的开始失重温度和失重时间比单独分析纯CaCO3的开始失重温度和失重时间分别降低85.9℃和提前13.3min,有利于脱硫反应的提前进行,延长了脱硫反应时间且降低了能耗;在煅烧温度为900℃时,碳酸钙/铜渣复合固硫剂比表面积达到最大值8.799m2/g,与单独分析纯CaCO3的比表面积5.00m2/g相比,其增幅达75.98%。     

真空钙热还原法制备金属钛粉的研究

在真空炉中(30~40 Pa)1273 K下,将物料放入螺纹密封的石墨坩埚中进行不同时间下的还原反应。本文采用热力学分析及X射线衍射、扫描电子显微镜及能量弥散X射线谱等方法与手段,系统研究了金属钙(Ca)与反应器中的氧气(O2)、氮气(N2)、二氧化钛(TiO2)的反应和还原时间及还原产物的预处理对得到金属钛粉(Ti)的影响。通过热力学研究,在温度低于钙的熔点(1115 K)时,密封容器内的O2与Ca的反应及N2与Ca的反应满足反应发生的热力学条件。当温度达到1273K时,Ca的饱和蒸气压p*≈p系,有利于整个气固反应进行。实验研究表明,在还原反应发生前,反应器内的O2,N2与Ca反应完全。将在1273 K下还原时间为4 h得到的还原产物在酸洗前真空挥发处理还原产物表面大量的Ca时,金属单质Ti再次被氧化成低价氧化物,最终得不到金属Ti粉。将反应时间延长至6 h时,酸洗过滤后得到形状不规则、纯度达到98.64%的Ti粉。     

Copper slag as sand replacement for high performance concrete

This paper reports on an experimental program to investigate the effect of using copper slag as a replacement of sand on the properties of high performance concrete (HPC). Eight concrete mixtures were prepared with different proportions of copper slag ranging from 0% (for the control mix) to 100%. Concrete mixes were evaluated for workability, density, compressive strength, tensile strength, flexural strength and durability. The results indicate that there is a slight increase in the HPC density of nearly 5% with the increase of copper slag content, whereas the workability increased rapidly with increases in copper slag percentage. Addition of up to 50% of copper slag as sand replacement yielded comparable strength with that of the control mix. However, further additions of copper slag caused reduction in the strength due to an increase of the free water content in the mix. Mixes with 80% and 100% copper slag replacement gave the lowest compressive strength value of approximately 80 MPa, which is almost 16% lower than the strength of the control mix. The results also demonstrated that the surface water absorption decreased as copper slag quantity increases up to 40% replacement; beyond that level of replacement, the absorption rate increases rapidly. Therefore, it is recommended that 40 wt% of copper slag can used as replacement of sand in order to obtain HPC with good strength and durability properties.     

Origin and sedimentation of Cu-droplets sticking to spinel solids in pyrometallurgical slags

Cu-droplet losses in slags are an important problem in Cu-industry, limiting the metal recovery. An important cause responsible for the entrainment of copper droplet losses in slags is their sticking behaviour to spinel solids. In the present study, the interaction between spinel solids and Cu-droplets is investigated in an industrially relevant slag system (PbO–CaO–SiO₂–Cu₂O–Al₂O₃–FeO–ZnO) using two complementary experimental set-ups. Firstly the influence of the sedimentation time is studied and secondly the presence of entrained (sticking) droplets is studied as a function of height in the slag layer. Based on the experimental results, a mechanism that explains the sticking Cu-droplets is proposed. Finally, a model describing the sedimentation of sticking and non-sticking droplets is formulated based on the experimental data.     

Investigation of the reduction kinetics of wustite fine powders

The reduction of wustite (FeO) by hydrogen was investigated over the temperature range 723 to 873 K. The reduction mechanism was found to depend on temperature relative to an effective eutectoid decomposition temperature of 803 K. Above this temperature the reaction proceeds directly according to: FeO + H₂ = Fe + H₂O while below this temperature the reduction is accomplished through the following two sequential steps: 4FeO = Fe + Fe₃O₄ and Fe + Fe₃O₄ + 4H₂ = 4Fe + 4H₂O. Approximate activation energies for reduction above and below 803 K were determined to be 51 and 58 kJ mol^–1, respectively. Investigations were also conducted on the oxidation of the iron resulting from the reduction of FeO.     

PRODUCTION OF Cu-Cr ALLOYS BY IN SITU REDUCTION OF CHROMIUM OXIDE DURING ELECTRO SLAG CRUCIBLE MELTING (ESCM)

An electro slag crucible melting process for production of copper-chromium alloys is described. The process uses fine copper scrap as a raw material. After the copper scrap is melted, chromium is alloyed with copper by direct reduction of chromium oxide added to the slag. Carbon and aluminum can be used as reductants and the reduction is carried out in situ in the molten slag. Copper chromium ingots containing up to ∼1 wt % chromium were produced by this process. The process serves the dual purpose of recycling copper scrap and alloying remelted copper by chromium. This is the first time that direct reduction has been employed during an electro slag melting process. The in situ reduction technique described has the potential of being a production route for a variety of alloys. It is particularly suitable for production of difficult-to-melt alloys such as copper-chromium.     

Investigation of high ferriferous sulphide lead concentrates processing technology

This article is dedicated to the investigations of the individual complex processing of the high ferriferrous sulphide lead concentrates by the way of lead blast furnace reducing melting. The data of the trials series of high ferriferrous lead sinters' reduction melting with the operating blast furnace have been presented. The results of investigations indicate that low lead losses with the slag (1.4÷1.8 wt.‐%) can be achieved by maintaining a slag composition of 38.4÷41.1 wt.‐% FeO and 0.70÷0.74 CaO/SiO₂ ratio, with a lead sinter throughput – 55÷60 tonnes/m² · day. The slag liquidus temperature is estimated to be ?1170°C.     

A study on the interfacial tension between solid iron and CaO–SiO<Subscript>2</Subscript>–MO system

Interfacial tension is an important property that plays an essential role in understanding wetting behavior between refractories–molten slag–steel in the steelmaking process. Most work on interfacial tensions of molten slag system have been done to clarify the effect of surface active elements in molten metal and slag composition, but there has been little work done with respect to the slags ionic structure. In this study, the interfacial tension between molten slag and solid Fe was investigated to understand the effect of the ionic structure of molten slag on interfacial tension by using solid Fe instead of molten steel. Interfacial tension measurements in CaO–SiO₂–FeO and CaO–SiO₂–MnO slags were carried out at 1,773 K on interstitial free (IF)-steel substrates using the sessile drop method. The composition of the slag was varied with amphoteric oxides of either FeO or MnO at unit basicity (C/S = 1.0). Results indicated a decrease in the interfacial tension with increased amphoteric oxide additions. The ionic species of molten slags were analyzed by FT-IR and the various types of oxygen ions (O²⁻, O⁻, O⁰⁾ in the slag was determined by X-ray photoelectron spectroscopy. The silicate bonding degree and the slags ionic behavior were semi-quantitatively analyzed with respect to the slag’s ionic structure model. By dissociating the slags networking structure with increased free oxygen ions, the interfacial tension decreased. Considering the ionic theory of molten slags, results indicate that the interfacial properties are directly affected by the ionic structure of the slag. This work hopes to clarify the relationship between the interfacial tension and the distribution of various oxygen ions.     

Hot corrosion mechanism of tundish plaster with steel slags in continuous casting

This study concerns the chemical reactions involved and the phases formed during penetration of slags of variable composition into porous plaster structure of tundish. Tundish plaster is mainly composed of MgO with minor amounts of SiO₂ and impurities, with a grain size of less than 1 mm, inorganic or organic fibers in order to decrease density and provide porosity for insulation, plasticizers and stiffening agents and some other additions. Tundish slag analysis for different grades of steel (7176D and 1191D, according to DIN standard) at different sequences, indicated a very variable composition of CaO (11–42%), SiO₂ (28–46%), Al₂O₃ (6–12%), MgO (11–20%), MnO (0–13%) and some minor variations of Fe, FeO and TiO₂. Experimental work indicated that slag when penetrated into pores of plaster, develop the phases of Monticellite (CaO · MgO · SiO₂) and Merwinite (CaO_1.5 · MgO_0.5 · SiO₂) around MgO particles and decrease the liquidus temperature from 2,800 °C to about 1,500 °C and provide dissolution of MgO grains in steel making process. Calculation based on two kinetic equations developed for diffusion controlled dissolution, indicated that the dissolution of MgO in tundish plaster is not a diffusion controlled process and is affected by turbulent flow parameters. Phase diagram of CaO–SiO₂–MgO indicates that decreasing SiO₂ to below 20% and increasing CaO content to as high as possible, increases the liquidus temperature to above 2,000 °C. Sources of SiO₂ in the process are the rice husk addition, which is used as an insulating material on top of the melt, and the slag flux addition. These sources should be reduced to as low a level as possible. This fact does not affect the fluidity of slag which is required for inclusion removal. Fluidity of slag comes from low melting point eutectics in CaO–Fe₂O₃ and CaO–FeO (about 1,200 °C) due to iron oxide on top of the steel melt.     

Cleaning of a copper matte smelting slag from a water-jacket furnace by direct reduction of heavy metals

Cleaning experiments of a copper matte smelting slag from the water-jacket furnace was undertaken by direct reduction in a laboratory-scale electric furnace. The effects of coal-to-slag ratio, w, and the reduction time, t, were considered for two different coal/slag mixing procedures. In the first procedure, metallurgical coal was added to the molten slag, whereas in the second procedure, coal was premixed with the solid slag before charging into the furnace. The recovery of heavy metals (Cu, Co), and the fuming of Pb and Zn were investigated. Contamination of the metal phase by iron and the acidity index of the final slag were analysed as these may impede the economical viability of the process. The lower w value of 2.56% yielded a recovery rate of less than 60% for copper and less than 50% for cobalt, and around 70% for zinc. However, increasing w to 5% allowed the recovery of 70-90% for Cu, Co and Zn simultaneously after 30-60 min reduction of the molten slag. After reduction, the cleaned slags contained only small amounts of copper and cobalt (<0.4 wt%). Fuming of lead and zinc was efficient as the %Pb of the residual slag dropped to levels lower than 0.04% after 30 min of reduction. Ninety percent of the lead was removed from the initial slag and collected in the dusts. The zinc content of the cleaned slags quickly dropped to between 1 and 3 wt% from the initial 8.2% after 30 min reduction for w value of 5 and after 60 min reduction for w value of 2.56. The dusts contained about 60% Zn and 10% Pb. Recovery of lead from fuming of the slag was higher than 90% in all the experimental conditions considered in this study.     

Phase relations in the aluminothermic reduction of ZrO<Subscript>2</Subscript>

This paper presents thermodynamic evaluation of reactions between ZrO₂ and aluminum, which indicates that the aluminothermic reduction of zirconium oxides at temperatures above 600°C is only possible when Al _x Zr _y intermetallic compounds form in the metallic phase. Thermodynamic analysis results are supported by experimental data, which demonstrate that, at ZrO₂: Al ratios in the range 0.4–1.4, the aluminothermic reduction of ZrO₂ leads predominantly to the formation of the congruently melting compounds Al₂Zr and Al₃Zr. The phase formation in the slag yields various forms of calcium aluminates and calcium zirconates and leads to a gradual reduction in the oxidation state of the zirconium.