Titanium leaching from red mud by diluted sulfuric acid at atmospheric pressure

Laboratory-scale research has focused on the recovery of titanium from red mud, which is obtained from bauxite during the Bayer process for alumina production. The leaching process is based on the extraction of this element with diluted sulfuric acid from red mud under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The titanium recovery efficiency on the basis of red mud weight reached 64.5%. The characterization of the initial red mud, as well as this of the leached residues was carried out by X-ray diffraction, TG-DTA and scanning electron microscopy.     

Experimental and mechanism research of the effects of alkali on the reduction reaction of hematite during roasting reduction reaction

Red mud as one of the major waste materials, the recycling of it is very important for environmental security and resource recovery. However, the alkali in the red mud strongly affects the concentrating of iron. In order to make the reduction process more controllable and enhance the efficiency, this paper studied the roasting reduction reaction behavior of hematite and artificially mixed red mud in different alkaline environments. X-ray diffraction (XRD), vibrating Sample Magnetometer (VSM) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) were used to reveal the phase transformation, magnetic transformation and microstructure variation of the roasting products. The results revealed that the optimum reduction temperature and time of hematite in alkaline environment were 560 °C and 15 min respectively. With the increase of NaOH and Na₂SiO₃, the phase transformation from Fe₂O₃ to Fe₃O₄ of hematite was hindered. The depression effect of NaOH was stronger than that of Na2SiO3. However, with the increase of CaO, Na₂SiO₃/CaO and NaOH/CaO, the phase transformation from Fe₂O₃ to Fe₃O₄ in hematite was enhanced first, and then depressed. The gangue minerals in artificially mixed red mud involved in the reaction and consumed part of alkali. The morphology evolution of hematite was similar under different condition that reduction reaction in cracked region was more sufficient.     

Recovery of iron from vanadium tailings with coal-based direct reduction followed by magnetic separation

A technique with coal-based direct reduction followed by magnetic separation is presented in this study for recovering and reusing iron otherwise wasted in vanadium tailings. Process parameters such as usage of additives, tailings/reductant/additives ratio, reduction temperature and time, as well as particle size were experimentally determined. The optimum process parameters were proposed as follows: using lime as the additive, lignite as the reductant, weight ratios of vanadium tailings/lignite/lime at 100:30:10, reduction roasting at 1200 °C for 60 min, and particle size of 98% less than 30 μm in the final roasted product feeding to magnetic separation. Under these conditions, a magnetic concentrate containing 90.31% total iron and 89.76% metallization iron with a total iron recovery rate of 83.88% was obtained. In addition, mineralography of vanadium tailings, coal-based reduction product and magnetic concentrate were studied by X-ray powder diffraction technique (XRD). The microstructures of above products were analyzed by scanning electron microscope (SEM) to help understand the mechanism.     

Red mud addition in the raw meal for the production of Portland cement clinker

The aim of the present research work was to investigate the possibility of adding red mud, an alkaline leaching waste, which is obtained from bauxite during the Bayer process for alumina production, in the raw meal for the production of Portland cement clinker. For that reason, two samples of raw meals were prepared: one with ordinary raw materials, as a reference sample ((PC)Ref), and another with 3.5% red mud ((PC)R/M). The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1350, 1400 and 1450 degrees C. Subsequently, the clinkers were produced by sintering the two raw meals at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the red mud did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the red mud did not negatively affect the quality of the produced cement.     

Lime-stabilized red mud bricks

Red mud is a waste material obtained from the aluminium extraction industry and consists mainly of the oxides of aluminium, iron and titianium. The present red mud production in the country is above two million tons every year, which is not being put to any worthwhile use except as a filler to a small extent in the preparation of roads. Efforts have been made at CBRI to produce burnt clay bricks by partially replacing the clay with red mud and fly-ash. In this process, the red mud is expected to find a major use shortly. Efforts have also been made to incorporate in the red mud a small percentage of lime and compress the mix at optimum moisture content in the form of bricks with a purpose of examining their strength and stability to the erosive action of water. A maximum wet compressive strength of 3.75 MN m^?2 with 5% lime and 4.22 MN m^?2 with 8% lime has been obtained after 28 days of casting and humid curing in the month of August. The red mud sample studied was obtained from the Indian Aluminium Company. The brick samples were studied for accelerated weathering and found suitable for use as a walling material for low-cost shelters. Modifications in the red mud mix, especially from the viewpoint of particle size distribution, have also been examined simultaneously by its part replacement with coarse-grained soil and fly-ash. The results indicate that the basis of the beneficial action of lime on red mud is predominantly chemical.     

Characterization of red mud derived from a combined Bayer Process and bauxite calcination method

Red mud can be derived from the processing of bauxite using different methods. The chemical and mineralogical composition of the combined Bayer Process and bauxite calcination red mud (BPBCRM) differs markedly from those of the pure Bayer Process red mud (PBPRM). In this study, red mud derived from a combined Bayer Process and bauxite calcination method was characterized. The results show that pH of the red mud decreased with increasing duration of storage time. Na dominated among the soluble cations, but the concentration of soluble Na decreased with increasing duration of storage time as a result of leaching. Cation exchange capacity also decreased with increasing duration of storage time, probably due to a decrease in pH causing a reduction in negatively charged sites on the red mud particles. Ca was the predominant exchangeable cation in the fresh red mud but the concentration of exchangeable Ca markedly decreased in the old red mud, which was dominated by exchangeable Na. The degree of crystallization and thermal stability of the red mud increased with increasing duration of storage. The acid neutralizing capacity of red mud obtained from this study was about 10 mol kg(-1), which is much greater than the reported values for the pure Bayer Process red mud. Column filtering experiment indicates that the red mud also had a very strong capacity to remove Cu, Zn and Cd from the filtering solution. It is conservatively estimated that the simultaneous removal rates of Cd, Zn and Cu by red mud are over 22,250 mg kg(-1), 22,500 mg kg(-1) and 25,000 mg kg(-1), respectively. The affinity of these metals to the red mud was in the following decreasing order: Cu>Zn>Cd. In general, the fresh red mud retained more heavy metals than the old red mud did.     

Recovery of alumina and alkali in Bayer red mud by the formation of andradite-grossular hydrogarnet in hydrothermal process

Bayer red mud (RM) is an alumina refinery waste product rich in aluminum oxides and alkalis which are present primarily in the form of sodium hydro-aluminosilicate desilication product (DSP). A hydrothermal process was employed to recover alumina and alkali from "Fe-rich" and "Fe-lean" RM, the two representative species of RM produced in China. The hydrothermal process objective phase is andradite-grossular hydrogarnet characterized by the isomorphic substitution of Al and Fe. Batch experiments were used to evaluate the main factors influencing the recovery process, namely reaction temperature, caustic ratio (molar ratio of Na(2)O to Al(2)O(3) in sodium solution), sodium concentration and residence time. The results revealed that the Na(2)O content of 0.5 wt% and A/S of 0.3 (mass ratio of Al(2)O(3) to SiO(2)) in leached residue could be achieved with Fe-rich RM under optimal conditions. However, the hydrothermal treatment of Fe-lean RM proved less successful unless the reaction system was enriched with iron. Subsequent experiments examined the effects of the ferric compound's content and type on the substitution ratio.     

火法焙烧蛇纹石制取氢氧化镁工艺研究

改变传统的酸浸取法,研究添加硫酸铵火法焙烧蛇纹石以浸出镁的适宜工艺条件,并用该法制备超细氢氧化镁,对试验中消耗的硫酸铵进行回收,并测试回收后的焙烧再用效果。结果表明,在本实验设计的工艺流程下蛇纹石中镁元素的一次烧出率可以达到62.42%,制备的超细氢氧化镁的白度可达99.8%,二次粒径d50≤10μm,硫酸铵回收率为55%,但返回焙烧再用效果较好。     

Galvanic sludge metals recovery by pyrometallurgical and hydrometallurgical treatment

This paper reports a study, on laboratory scale, of sulphating roasting to perform a treatment for a selective recovery of valuable metals from galvanic sludge. The target metals were copper, zinc and nickel and the sulphating agent used was pyrite, from coal wastes. The particularity of this treatment is the use of two hazardous wastes as raw material. They are generated in large quantities at coal extraction sites (coal wastes) and at plating shops (galvanic sludge). The wastes were characterized by X-ray fluorescence (XRF), particle size distribution and water contents. The chemical characterization showed sludges with high copper concentration, with more than 14% (dry base). In the roasting step, the galvanic sludge was mixed with pyritic waste and the parameters evaluated were galvanic sludge/pyrite ratio, roasting temperature and roasting time. After roasting, the product of reaction was leached with water in room temperature for 15 min. Considering that other studies have already demonstrated that the pyrometallurgical step determines the process efficiency, this paper only reports the influence of pyrometallurgical parameters. Hydrometallurgical processes will be better evaluated in further studies. The conditions that best reflect a compromise between the valuable metal recover and the economical viability of the process were achieved for 1:0.4 galvanic sludge/pyrite ratio, 90 min of roasting time and 550 degrees C of roasting temperature. These conditions lead to a recovery of 60% zinc, 43% nickel and 50% copper.     

The potential application of red mud in the production of castings

The bauxite industry in Jamaica is the third largest producer of alumina in the world. Because of the technological method of processing the bauxite, there is a large amount of the world's red mud residue being disposed in Jamaica. The magnitude of the industry's production of alumina and the red mud disposal problem as a by-product is of the same order.

This research was conducted to investigate the feasibility of using a mixture of red mud and the traditional silica sand to produce quality-casting component.

The porosity of the aluminium specimens obtained from the red mud castings showed that porosity increased up to two-fold, depending on the ratio of sand and red mud. For applications where optimum casting strength is important, the use of 100% red mud may be unsatisfactory.

Although there are other variables that affect the quality of the mixture of silica sand and red mud mould in castings, the result is very significant given the possibility of applying portions of red mud in other casting techniques.     

Mineralogical reconstruction of Titanium-Vanadium hematite and magnetic separation mechanism of titanium and iron minerals

In this paper, magnetization roasting - low-intensity magnetic separation was performed on a pre-concentration concentrate obtained from an Australian hematite containing titanium and vanadium to realize the separation of titanium and vanadium. The results showed that an iron concentrate with TFe (total iron) grade of 58.71%, iron recovery of 86.72% and V₂O₅ grade of 1.00%, V₂O₅ recovery of 93.97% could be obtained under the optimum roasting conditions (roasting temperature of 580 °C, total gas-flow rate of 1.44 m³/h, CO concentrate of 30%, roasting time of 20 min), meanwhile the iron tailings (i.e., TiO₂ concentrate) with TiO₂ grade of 43.76%, TiO₂ recovery of 63.42% was obtained. XRD analysis, phase iron chemical analysis, and magnetic analysis were conducted on the raw sample and the roasted products. The results showed that after magnetization roasting, the hematite and limonite in raw sample were transformed into magnetite with strong magnetism, and the vanadium hematite of hexagonal system was transformed into vanadium magnetite of equiaxed system. As the weakly magnetic ilmenite does not participate in the reaction during reduction roasting, the separation of ilmenite and vanadium can be easily achieved via magnetic separation.     

Radiological aspects of the usability of red mud as building material additive

Several researchers have examined and achieved favourable results in connection with the building industry's use of red mud extracted in large quantities from the processing of bauxite. These days more and more precedence is being given to limiting the radiological dose to the population. In this study carried out in Hungary, the use of red mud, bauxite, and clay additives recommended for the production of special cements, were examined from a radiological aspect.

²²⁶Ra and ²³²Th activity concentrations measured in Hungarian bauxite, red mud and clay samples were significantly similar with the levels for such raw materials mentioned in international literature.

Taking radiation protection aspects into consideration, none of these products can be directly used for building construction. Taking Hungarian and international values into consideration, a small amount of red mud, not exceeding 15% could be used for brick production, for example as a colouring material. However, beyond this amount the standards for building materials would not be met.

For the production of cements an even stricter limit needs to be determined when both bauxite and red mud are used.     

Multi-functional honeycomb ceramic materials produced from bauxite residues

Red mud is a hazardous waste produced by the Bayer process during commercial production of alumina. In this study, red mud is recycled to produce industrial honeycomb ceramic materials. The materials and processing parameters including the type and size the pore-forming agent, sintering temperature, and stripping methodology are studied. The optimal sintering temperature is determined to be 1075 °C. The bending strength, porosity, water absorption capacity, and bulk density are investigated by X-ray diffraction and scanning electron microscopy. The bending strength exceeds 32.66 MPa after addition of calcium carbonate but the porosity and water absorption capacity diminish to 28.6% and 12.6%, respectively. Incorporation of coal powders increases the porosity and water absorption capability to 36.0%, 20.24%, respectively, but the bending strength drops to 21.69 MPa.     

Partial magnetization of siderite via fluidization roasting for efficient recovery of iron: Phase transition,microstructure evolution and kinetics

This study proposes a new process for the partial magnetization of siderite using fluidization roasting, addressing its difficult beneficiation characteristics and lack of large-scale exploitation. Two siderite samples, designated sample S45 and sample S74, with particle sizes of 45–74 μm and 74–150 μm, respectively, were used to optimize the process parameters. The fluidization roasting process rapidly converted siderite to ferromagnetic magnetite, with the magnetite distributed on particle surfaces and internal cracks. CO₂ was used during roasting to facilitate the transformation of siderite to magnetite. The iron recovery reached more than 98 % when the roasting time was only 2 min for sample S45 (or 4 min for sample S74). Partial magnetization of siderite can be achieved in a short time by fluidization roasting with low energy consumption for efficient iron recovery. The isothermal kinetics indicate that the kinetic mechanism of the two siderite samples was the random nucleation and growth model, with the fine-grained sample having a shorter reaction time and lower activation energy.     

The mechanism of suspension reduction on Fe enrichment with low-grade carbonate-containing iron ore

Carbonate-containing iron ore is a refractory iron resource with a complex symbiotic relationship between iron minerals and gangue. An efficient suspension magnetizing roasting technology was proposed to extract the iron mineral from the carbonate-containing iron ore. The results demonstrated that a concentrate containing 67.20% total Fe and 83.35% iron recovery was obtained under the optimal conditions: the roasting temperature at 550 °C for 15 min with a CO concentration of 15 at.%, a total gas flow of 400 mL/min, and the grinding size of the roasted product was ?0.045 mm accounting for 85.39 wt%. The phase transformation and microstructure evolution of the samples before and after roasting were characterized. The investigation revealed that the iron mineral phases were selectively transformed from weakly magnetic hematite and siderite to strongly magnetic magnetite, disrupting the particle structure. Subsequently, the iron mineral was effectively enriched into concentrate via magnetic separation.     

Carbothermic reduction roasting for processing of ferruginous chromite ore using conventional and microwave heating

The present study investigates the recovery of chromite from a low-grade ferruginous ore through the carbothermic magnetization route using conventional and microwave heating sources. The carbothermic magnetization of ore is studied in both a horizontal tube furnace and a microwave oven by varying different process variables. The main objective of the study is to enhance the magnetic susceptibility of iron-bearing gangue minerals to enable the separation in a magnetic field. Alteration of crystalline structure and magnetic property of these minerals enables separation of low-grade ore by using magnetic separation. It is found that low-grade ferruginous chromite ore can be upgraded by reduction roasting, and 61.2% Cr₂O₃ was recovered with a chromium-to-iron ratio of 1.93 from a feed chromium-to-iron ratio of 1.01. The optimum result is achieved at a roasting temperature of 800 °C, with a roasting time of 60 min and a reductant dosage of 7.5%. Similarly, under microwave radiation, the chromium-to-iron ratio was upgraded to 1.81 with a recovery of 22%Cr₂O₃. The optimum result achieved under microwave radiation is at a microwave power of 900 W and exposure time of 7.5 min, with a reductant dosage of 10%. The findings of these two processing routes are discussed through characterization tools.     

Reuse of a treated red mud bauxite waste: studies on environmental compatibility

Red mud is the major solid waste produced in the process of alumina extraction from bauxite (Bayer process). Environmental "compatibility" of a treated red mud was studied in order to evaluate its possible recycling in environmental compartments. The leaching test requested by the Italian law on treated solid waste to be "re-introduced in the environment" was performed on this material. Moreover, in order to better evaluate the environmental compatibility, three different types of eco-toxicological tests were applied (Microtox test, ASTM microalgae toxicity test and sea urchin embryo toxicity test). These "chemical" and eco-toxicological tests gave encouraging results. The possibility to use this material for treating contaminated waters and soils was evaluated, again with particular attention to the Italian regulatory system, through experiments on the treated red mud metal trapping ability and on the subsequent release of trapped metals, at low pH conditions. The treated red mud showed a general high metal trapping capacity and the release at low pH was generally low.     

铝灰渣与废盐酸制备聚合氯化铝的试验研究

以铝灰渣和废盐酸为原料,通过酸溶法制备聚合氯化铝,考察了原料配比、反应温度、反应时间、熟化温度、熟化时间等因素对聚合氯化铝性能的影响,并对最佳工艺参数条件下制备的聚合氯化铝进行红外光谱分析。结果表明,铝灰渣和废盐酸制备聚合氯化铝的最佳工艺参数为:原料配比为m∶V1∶V2=20∶55∶80,反应温度为85℃,反应时间为3.5 h,熟化温度为80℃,熟化时间为42 h;在此条件下,制备的聚合氯化铝中氧化铝质量分数为8.15%,盐基度为35.6%;红外光谱分析表明合成的聚合氯化铝中存在聚合态铝和羟基结构。     

Use of fly ash,phosphogypsum and red mud as a liner material for the disposal of hazardous zinc leach residue waste

Increasing amounts of residues and waste materials coming from industrial activities in different processes have become an increasingly urgent problem for the future. The release of large quantities of heavy metals into the environment has resulted in a number of environmental problems. The present study investigated the safe disposal of the zinc leach residue waste using industrial residues such as fly ash, phosphogypsum and red mud. In the study, leachability of heavy metals from the zinc leach residue has been evaluated by mine water leaching procedure (MWLP) and toxicity characteristic leaching procedure (TCLP). Zinc removal from leachate was studied using fly ash, phosphogypsum and red mud. The adsorption capacities and adsorption efficiencies were determined. The adsorption rate data was analyzed according to the pseudo-second-order kinetic, Elovich kinetic and intra-particle diffusion kinetic models. The pseudo-second-order kinetic was the best fit kinetic model for the experimental data. The results show that addition of fly ash, phosphogypsum and red mud to the zinc leach residue drastically reduces the heavy metal content in the leachate and could be used as liner materials.     

Defluoridation of groundwater using brick powder as an adsorbent

Defluoridation of groundwater using brick powder as an adsorbent was studied in batch process. Different parameters of adsorption, viz. effect of pH, effect of dose and contact time were selected and optimized for the study. Feasible optimum conditions were applied to two groundwater samples of high fluoride concentration to study the suitability of adsorbent in field conditions. Comparison of adsorption by brick powder was made with adsorption by commercially available activated charcoal. In the optimum condition of pH and dose of adsorbents, the percentage defluoridation from synthetic sample, increased from 29.8 to 54.4% for brick powder and from 47.6 to 80.4% for commercially available activated charcoal with increasing the contact time starting from 15 to 120 min. Fluoride removal was found to be 48.73 and 56.4% from groundwater samples having 3.14 and 1.21 mg l(-1) fluoride, respectively, under the optimized conditions. Presence of other ions in samples did not significantly affect the deflouridation efficiency of brick powder. The optimum pH range for brick powder was found to be 6.0-8.0 and adsorption equilibrium was found to be 60 min. These conditions make it very suitable for use in drinking water treatment. Deflouridation capacity of brick powder can be explained on the basis of the chemical interaction of fluoride with the metal oxides under suitable pH conditions. The adsorption process was found to follow first order rate mechanism as well as Freundlich isotherm.