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Compared with conventional roasting and magnetic separation processes, higher reduction temperatures and stronger reducing atmospheres are used in direct reduction technologies to reduce iron oxides to metallic iron, which is often liberated during reduction and amenable to magnetic separation. Reduction and magnetic separation of an Australian refractory iron ore was therefore studied as a function of reduction temperature, time and coal addition. It was found that during reduction, the particle size of the reduced iron increased with reduction temperature and time. Subsequent magnetic separation tests were conducted on the reduction products. A reduced iron powder with an Fe grade of 85.67% was obtained at an Fe recovery of 87.82% under optimum reduction conditions where a metallisation rate of 85.82% was achieved. The mechanism involved in the reduction is discussed from X-ray diffraction and scanning electron microscopy results., Compared with conventional roasting and magnetic separation processes, higher reduction temperatures and stronger reducing atmospheres are used in direct reduction technologies to reduce iron oxides to metallic iron, which is often liberated during reduction and amenable to magnetic separation. Reduction and magnetic separation of an Australian refractory iron ore was therefore studied as a function of reduction temperature, time and coal addition. It was found that during reduction, the particle size of the reduced iron increased with reduction temperature and time. Subsequent magnetic separation tests were conducted on the reduction products. A reduced iron powder with an Fe grade of 85.67% was obtained at an Fe recovery of 87.82% under optimum reduction conditions where a metallisation rate of 85.82% was achieved. The mechanism involved in the reduction is discussed from X-ray diffraction and scanning electron microscopy results.

Vanadium-titanium magnetite from Panzhihua (Sichuan, China) was crushed by high pressure grinding roller (HPGR) and particle size characteristics of the crushed product and the micro-cracks generated were compared with those from a jaw crusher. Results showed that change in particle size in the HPGR was closely related to the pressure on the surface of the roller: the coarse particles were preferentially crushed as pressure increased, the coefficient of uniformity decreased, and the particle size distribution was more uniform. The content of fines was significantly higher in the HPGR than from the jaw crusher. More microcracks were produced in the HPGR than the jaw crusher, mainly stress cracks, intra-crystalline cracks and cleavage cracks. The specific surface area of the grain size of -0.074 mm of the products crushed by HPGR was improved by 38.18% and the Bond grinding work index (objective particle size was 0.074 mm) of ore crushed by HPGR was lower than that crushed by jaw crusher. The liberation degree of monomer of the product crushed by HPGR was higher than from the jaw crusher with a similar fineness of grinding., 5 refs., Vanadium-titanium magnetite from Panzhihua (Sichuan, China) was crushed by high pressure grinding roller (HPGR) and particle size characteristics of the crushed product and the micro-cracks generated were compared with those from a jaw crusher. Results showed that change in particle size in the HPGR was closely related to the pressure on the surface of the roller: the coarse particles were preferentially crushed as pressure increased, the coefficient of uniformity decreased, and the particle size distribution was more uniform. The content of fines was significantly higher in the HPGR than from the jaw crusher. More microcracks were produced in the HPGR than the jaw crusher, mainly stress cracks, intra-crystalline cracks and cleavage cracks. The specific surface area of the grain size of -0.074 mm of the products crushed by HPGR was improved by 38.18% and the Bond grinding work index (objective particle size was 0.074 mm) of ore crushed by HPGR was lower than that crushed by jaw crusher. The liberation degree of monomer of the product crushed by HPGR was higher than from the jaw crusher with a similar fineness of grinding.

The flotation behaviour of the boron mineral camsellite from Fengcheng, Liaoning Province, China was investigated using the pure mineral with various collectors and depressants at different dosages and pHs. Results showed that at pH 8.5-9.5, 90-93.5% recovery could be achieved with dodecylamine and 84-86% with sodium oleate. The adsorption of the former was not affected by the addition of sodium hexametaphosphate but with the latter adsorption was depressed. When starch was used as the depressant, flotation of camsellite was almost completely suppressed in alkaline conditions; significant depression was also observed when calcium chloride was added. The higher the slurry pH, the greater the depression. Zeta potential measurements indicated that flotation was mainly initiated by the electrostatic adsorption of the collector on the mineral. XPS analysis showed that dodecylamine had a higher surface coverage than sodium oleate., The flotation behaviour of the boron mineral camsellite from Fengcheng, Liaoning Province, China was investigated using the pure mineral with various collectors and depressants at different dosages and pHs. Results showed that at pH 8.5-9.5, 90-93.5% recovery could be achieved with dodecylamine and 84-86% with sodium oleate. The adsorption of the former was not affected by the addition of sodium hexametaphosphate but with the latter adsorption was depressed. When starch was used as the depressant, flotation of camsellite was almost completely suppressed in alkaline conditions; significant depression was also observed when calcium chloride was added. The higher the slurry pH, the greater the depression. Zeta potential measurements indicated that flotation was mainly initiated by the electrostatic adsorption of the collector on the mineral. XPS analysis showed that dodecylamine had a higher surface coverage than sodium oleate.

The selective grinding of bauxite was investigated experimentally in ball and vibration mills, using a low-grade ore with aluminium to silicon ratio (A:S) of 4.4. Grinding efficiency, particle size distributions of ground products and distribution of alumina and silica were studied under various grinding conditions and optimal values for the parameters determined. The findings are discussed in terms of the mechanisms both of mineral liberation of diaspore from silicate minerals and of size reduction, as well as the influence of the operating parameters: grinding fineness, grinding pulp concentration, and ratio of grinding media to charge. For the ball mill and vibration mill respectively, the weight ratios of ground product with A:S greater than 7.5 are 27% and 25% and the recoveries of Al2O3 are 30% and 27%., The selective grinding of bauxite was investigated experimentally in ball and vibration mills, using a low-grade ore with aluminium to silicon ratio (A:S) of 4.4. Grinding efficiency, particle size distributions of ground products and distribution of alumina and silica were studied under various grinding conditions and optimal values for the parameters determined. The findings are discussed in terms of the mechanisms both of mineral liberation of diaspore from silicate minerals and of size reduction, as well as the influence of the operating parameters: grinding fineness, grinding pulp concentration, and ratio of grinding media to charge. For the ball mill and vibration mill respectively, the weight ratios of ground product with A:S greater than 7.5 are 27% and 25% and the recoveries of Al2O3 are 30% and 27%.

Separation efficiency in classification at fine sizes is usually very low, which leads to large recirculating loads and significant overgrinding. The Derrick Stack Sizer is a screening system that has overcome these problems and allows screening down to 200 mesh at high screening capacity. The features of the sizer are presented and the theoretical background to the improvements in performance is discussed, looking at the relationships between size classification, circulating load and mineral recovery. A simulation model to predict the improved performance is introduced. Benefits from the sizer's introduction include reduced circulating load and ball mill feed and hence increased grinding capacity, elimination of fines in the recycled feed thus reduction of overgrinding, and improved economic mineral recovery as a result of the micro-jigging effect of the screens' motion. Operational data from the iron ore industry indicate that as a result of the sizer's introduction to closed grinding circuits the circulating load was reduced from about 300% to 60%, whilst iron recovery has increased by 6-8%., Separation efficiency in classification at fine sizes is usually very low, which leads to large recirculating loads and significant overgrinding. The Derrick Stack Sizer is a screening system that has overcome these problems and allows screening down to 200 mesh at high screening capacity. The features of the sizer are presented and the theoretical background to the improvements in performance is discussed, looking at the relationships between size classification, circulating load and mineral recovery. A simulation model to predict the improved performance is introduced. Benefits from the sizer's introduction include reduced circulating load and ball mill feed and hence increased grinding capacity, elimination of fines in the recycled feed thus reduction of overgrinding, and improved economic mineral recovery as a result of the micro-jigging effect of the screens' motion. Operational data from the iron ore industry indicate that as a result of the sizer's introduction to closed grinding circuits the circulating load was reduced from about 300% to 60%, whilst iron recovery has increased by 6-8%.

Dong Anshan iron ore contains at depth increasing amounts of carbonates that adversely affect the anionic reverse flotation of haematite. In order to investigate this and devise a new flowsheet, the flotation properties of the main minerals martite (haematite), magnetite, quartz, siderite and ankerite were investigated. Results of single-mineral flotation experiments showed that the combination of starch and calcium chloride at different pHs can cause differences in flotability between the minerals. A new sequential flotation flowsheet based on this finding was explored in both closed and open circuit: carbonates are first collected under neutral conditions as siderite concentrate, useable for blast-furnace feed, and then quartz under alkaline conditions by a reverse flotation step to leave a haematite concentrate. The process was used successfully on a magnetic separation concentrate. EDS and SEM investigations showed that adsorption of fine siderite, which starch does not depress effectively, occurs on the surfaces of quartz and haematite, rendering their flotation behaviour similar; this is overcome in the revised route., Dong Anshan iron ore contains at depth increasing amounts of carbonates that adversely affect the anionic reverse flotation of haematite. In order to investigate this and devise a new flowsheet, the flotation properties of the main minerals martite (haematite), magnetite, quartz, siderite and ankerite were investigated. Results of single-mineral flotation experiments showed that the combination of starch and calcium chloride at different pHs can cause differences in flotability between the minerals. A new sequential flotation flowsheet based on this finding was explored in both closed and open circuit: carbonates are first collected under neutral conditions as siderite concentrate, useable for blast-furnace feed, and then quartz under alkaline conditions by a reverse flotation step to leave a haematite concentrate. The process was used successfully on a magnetic separation concentrate. EDS and SEM investigations showed that adsorption of fine siderite, which starch does not depress effectively, occurs on the surfaces of quartz and haematite, rendering their flotation behaviour similar; this is overcome in the revised route.

The chemical and mineralogical composition of slags arising from iron and steel desulphurisation by hot metal pre-treatment and from slag skimming was studied in order to determine their potential as iron- bearing raw materials and to suggest processing routes for iron recovery. A sample from Anshan Steel Works processed by hot metal pre-treatment was analysed chemically and by x-ray diffraction and SEM. The iron content was 54.18% and the sulphur content 1.01%. The sample included metallic iron, ferrite, wustite, metasilicates, aluminosilicates, aluminates, and lime. The iron is present mostly in strongly magnetic phases and is amenable to magnetic separation. Sulphur is concentrated in the smaller particles so classification would be effective for desulphurisation., The chemical and mineralogical composition of slags arising from iron and steel desulphurisation by hot metal pre-treatment and from slag skimming was studied in order to determine their potential as iron- bearing raw materials and to suggest processing routes for iron recovery. A sample from Anshan Steel Works processed by hot metal pre-treatment was analysed chemically and by x-ray diffraction and SEM. The iron content was 54.18% and the sulphur content 1.01%. The sample included metallic iron, ferrite, wustite, metasilicates, aluminosilicates, aluminates, and lime. The iron is present mostly in strongly magnetic phases and is amenable to magnetic separation. Sulphur is concentrated in the smaller particles so classification would be effective for desulphurisation.

A one-step carbonation method, bubbling pure CO2 gas into a suspension of calcium hydroxide in the presence of phosphoric acid, was investigated for the synthesis of needle-like aragonite. The influence was assessed of phosphoric acid dosage, reaction temperature, carbon dioxide flow rate, and initial concentration of calcium hydroxide. It was found that the presence of the phosphoric acid in the suspension results in the rapid formation of hydroxyapatite crystals which act as nuclei for the growth of aragonite. Acid additions with P:Ca of 0.2 to 0.3, temperature of 75 to 85 degrees C, low CO2 flow rate and initial solids concentration of 1. 5 to 5.6% are beneficial for the formation of aragonite. Well- crystallised needle-like whiskers with length greater than 20 microns and aspect ratios greater than 15 were directly synthesised., A one-step carbonation method, bubbling pure CO2 gas into a suspension of calcium hydroxide in the presence of phosphoric acid, was investigated for the synthesis of needle-like aragonite. The influence was assessed of phosphoric acid dosage, reaction temperature, carbon dioxide flow rate, and initial concentration of calcium hydroxide. It was found that the presence of the phosphoric acid in the suspension results in the rapid formation of hydroxyapatite crystals which act as nuclei for the growth of aragonite. Acid additions with P:Ca of 0.2 to 0.3, temperature of 75 to 85 degrees C, low CO2 flow rate and initial solids concentration of 1. 5 to 5.6% are beneficial for the formation of aragonite. Well- crystallised needle-like whiskers with length greater than 20 microns and aspect ratios greater than 15 were directly synthesised.

The hydration of synthetic calcium sulphate hemihydrate whiskers prepared using a hydrothermal method from natural gypsum was studied and contrasted with that of a so-called gypsum hemihydrate, which is of lower purity and contains more crystal defects. The surface topographies and shape of the hemihydrate whiskers and of hydrates produced were analysed by online electron beam observation and using x-ray diffraction. The results demonstrated the transformation of crystal type and shape and reduction in aspect ratio. The hydration mechanism is discussed in the light of the FTIR spectroscopy results. It is concluded that the hydration process consists of three stages: initial hydration, formation and coarsening of dihydrate whiskers, and formation of dihydrate with different crystal shapes. In contrast, hydration products of gypsum hemihydrate are formed during dissolution without transition products., The hydration of synthetic calcium sulphate hemihydrate whiskers prepared using a hydrothermal method from natural gypsum was studied and contrasted with that of a so-called gypsum hemihydrate, which is of lower purity and contains more crystal defects. The surface topographies and shape of the hemihydrate whiskers and of hydrates produced were analysed by online electron beam observation and using x-ray diffraction. The results demonstrated the transformation of crystal type and shape and reduction in aspect ratio. The hydration mechanism is discussed in the light of the FTIR spectroscopy results. It is concluded that the hydration process consists of three stages: initial hydration, formation and coarsening of dihydrate whiskers, and formation of dihydrate with different crystal shapes. In contrast, hydration products of gypsum hemihydrate are formed during dissolution without transition products.

The objective of the study was to prepare ultrafine calcium sulphate whiskers from gypsum (calcium sulphate dihydrate) and investigate their toughening effect in composites with polypropylene. Gypsum and water were mixed to a slurry and heated under pressure to produce the hemihydrate which was then dehydrated, dried and depolymerised. The influence of temperature, slurry concentration, raw material size and pH on the crystallisation process were assessed using SEM to examine the crystal morphology, and the optimal values were determined, at which crystals with diameter 0.19 microns and an aspect ratio of 98 could be produced. The dispersion behaviour of the calcium sulphate in the polypropylene matrix, the influence of different amounts of it, and the effect of treating the calcium sulphate with the surfactant titanate NDZ-401on the izod impact toughness of the composite were investigated., The objective of the study was to prepare ultrafine calcium sulphate whiskers from gypsum (calcium sulphate dihydrate) and investigate their toughening effect in composites with polypropylene. Gypsum and water were mixed to a slurry and heated under pressure to produce the hemihydrate which was then dehydrated, dried and depolymerised. The influence of temperature, slurry concentration, raw material size and pH on the crystallisation process were assessed using SEM to examine the crystal morphology, and the optimal values were determined, at which crystals with diameter 0.19 microns and an aspect ratio of 98 could be produced. The dispersion behaviour of the calcium sulphate in the polypropylene matrix, the influence of different amounts of it, and the effect of treating the calcium sulphate with the surfactant titanate NDZ-401on the izod impact toughness of the composite were investigated.

A microphone, a power sensor and a pressure sensor were used to measure the sound intensity, power consumption and bearing pressure inside a laboratory-sized ball mill via their external signals. Mathematical models were established to link the external signals to the internal parameters by multivariate regression analysis. Experimental results showed that parameters could be directly predicted from the tri- sensor measurements, providing a new method for optimising wet ball milling., A microphone, a power sensor and a pressure sensor were used to measure the sound intensity, power consumption and bearing pressure inside a laboratory-sized ball mill via their external signals. Mathematical models were established to link the external signals to the internal parameters by multivariate regression analysis. Experimental results showed that parameters could be directly predicted from the tri- sensor measurements, providing a new method for optimising wet ball milling.

The synthesis of crystalline zinc oxide nanoparticles with closely- controlled size and morphology by a precipitation-pyrolysis route is described. Zinc sulphate and oxalic acid are used as starting materials to prepare zinc oxalate dihydrate. Control of the particle size of this precursor by means of the precipitation agent is important in the production of well-dispersed zinc oxide particles in the subsequent pyrolysis stage in which dehydration of the oxalate and formation of the zinc oxide occur; the kinetics of these reactions are discussed and optimum conditions determined. A hydrometallurgical route for obtaining zinc sulphate by sulphuric acid/iron (III) sulphate leaching of zinc blende (sphalerite) concentrates with recycling of all wastes is proposed as part of the flowsheet., The synthesis of crystalline zinc oxide nanoparticles with closely- controlled size and morphology by a precipitation-pyrolysis route is described. Zinc sulphate and oxalic acid are used as starting materials to prepare zinc oxalate dihydrate. Control of the particle size of this precursor by means of the precipitation agent is important in the production of well-dispersed zinc oxide particles in the subsequent pyrolysis stage in which dehydration of the oxalate and formation of the zinc oxide occur; the kinetics of these reactions are discussed and optimum conditions determined. A hydrometallurgical route for obtaining zinc sulphate by sulphuric acid/iron (III) sulphate leaching of zinc blende (sphalerite) concentrates with recycling of all wastes is proposed as part of the flowsheet.

An oolitic haematite ore containing 1.31% P was reduced in the presence of coal at temperatures ranging from 1 473 to 1 548 K. The reduction behaviour of apatite, which is the only P-containing mineral in the ore, was studied at different reduction conditions based on the thermodynamic analysis. Thermodynamic calculation showed that the SiO2, Al2O3 or SiO2-Al2O3 could decrease the standard Gibbs free energy and initial temperature of the apatite reduction significantly. The initial temperature of the apatite reduction decreased from above 1 650 K to 1 497 K, 1 541 K and 1 419 K in the presence of SiO2, Al2O3 and SiO2-Al2O3, respectively. Experimental results indicated that the reduction conditions obviously affected the reduction behaviour of apatite. A higher reduction temperature, C/O molar ratio and a longer reduction time were favourable for the apatite reduction. The reduction degree of apatite reached 83.62% at 1 548 K with a C/O molar ratio of 2.5 and after 60 min reduction. In addition, the reduction kinetics of apatite was investigated by common order reactions, and the corresponding kinetic parameters were computed according to the Arrhenius function. The results demonstrated that the most suitable mechanism for the apatite reduction was first-order reaction, and the apparent reaction rate of apatite reduction increased with increasing reduction temperature and C/O molar ratio. Furthermore, both the apparent activation energy and pre-exponential factor of apatite reduction decreased slightly with increasing C/O molar ratio. (Authors)., An oolitic haematite ore containing 1.31% P was reduced in the presence of coal at temperatures ranging from 1 473 to 1 548 K. The reduction behaviour of apatite, which is the only P-containing mineral in the ore, was studied at different reduction conditions based on the thermodynamic analysis. Thermodynamic calculation showed that the SiO2, Al2O3 or SiO2-Al2O3 could decrease the standard Gibbs free energy and initial temperature of the apatite reduction significantly. The initial temperature of the apatite reduction decreased from above 1 650 K to 1 497 K, 1 541 K and 1 419 K in the presence of SiO2, Al2O3 and SiO2-Al2O3, respectively. Experimental results indicated that the reduction conditions obviously affected the reduction behaviour of apatite. A higher reduction temperature, C/O molar ratio and a longer reduction time were favourable for the apatite reduction. The reduction degree of apatite reached 83.62% at 1 548 K with a C/O molar ratio of 2.5 and after 60 min reduction. In addition, the reduction kinetics of apatite was investigated by common order reactions, and the corresponding kinetic parameters were computed according to the Arrhenius function. The results demonstrated that the most suitable mechanism for the apatite reduction was first-order reaction, and the apparent reaction rate of apatite reduction increased with increasing reduction temperature and C/O molar ratio. Furthermore, both the apparent activation energy and pre-exponential factor of apatite reduction decreased slightly with increasing C/O molar ratio. (Authors).

An oolitic iron ore was isothermally reduced by coal at 1 423-1 573 K and the reduction kinetics investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48.26, 69.80 and 127.58 kJ/ mol respectively. The rate-controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate-controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction. (Authors.), An oolitic iron ore was isothermally reduced by coal at 1 423-1 573 K and the reduction kinetics investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48.26, 69.80 and 127.58 kJ/ mol respectively. The rate-controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate-controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction. (Authors.)

With the objective of phosphorus enrichment in the metallic iron during coal-based reduction, high-phosphorus oolitic haematite ore was reduced in the presence of coal with the coal/ore molar ratio (coal/ore, the molar ratio of fixed carbon in coal to oxygen in iron oxides of ore) varying from 1.0 to 2.5 at temperatures ranging from 1 473 to 1 548 K. The metallic iron was beneficiated from reduction products by magnetic separation. The results showed that the enrichment of phosphorus in the metallic iron improved with increasing temperature and coal/ore molar ratio. The phosphorus content and the phosphorus enrichment could reach 2.5 and 77.5%, respectively, with a coal/ore molar ratio of 2.5 at 1 548 K and after 60 minute reduction. The high phosphorus-containing metallic iron so obtained could then be converted to steel and high phosphorus steelmaking slag that can be used as a phosphate fertiliser. Kinetic analysis demonstrated that the process of phosphorus enrichment in the metallic iron could be divided into two stages, early and late, described by phase boundary-controlled reaction and diffusion-controlled, respectively. The effect of reduction temperature and coal/ore molar ratio on the enrichment behaviour of phosphorus in the metallic iron during coal-based reduction of high phosphorus-containing oolitic haematite ore was studied in this paper. Furthermore, the kinetic parameters of phosphorus enrichment in the metallic iron were determined through kinetic model fitting to provide scientific understanding of phosphorus enrichment behaviour during reduction of oolitic haematite ores. This will in turn boost the utilisation of high phosphorus-containing oolitic haematite ores. (Authors.), With the objective of phosphorus enrichment in the metallic iron during coal-based reduction, high-phosphorus oolitic haematite ore was reduced in the presence of coal with the coal/ore molar ratio (coal/ore, the molar ratio of fixed carbon in coal to oxygen in iron oxides of ore) varying from 1.0 to 2.5 at temperatures ranging from 1 473 to 1 548 K. The metallic iron was beneficiated from reduction products by magnetic separation. The results showed that the enrichment of phosphorus in the metallic iron improved with increasing temperature and coal/ore molar ratio. The phosphorus content and the phosphorus enrichment could reach 2.5 and 77.5%, respectively, with a coal/ore molar ratio of 2.5 at 1 548 K and after 60 minute reduction. The high phosphorus-containing metallic iron so obtained could then be converted to steel and high phosphorus steelmaking slag that can be used as a phosphate fertiliser. Kinetic analysis demonstrated that the process of phosphorus enrichment in the metallic iron could be divided into two stages, early and late, described by phase boundary-controlled reaction and diffusion-controlled, respectively. The effect of reduction temperature and coal/ore molar ratio on the enrichment behaviour of phosphorus in the metallic iron during coal-based reduction of high phosphorus-containing oolitic haematite ore was studied in this paper. Furthermore, the kinetic parameters of phosphorus enrichment in the metallic iron were determined through kinetic model fitting to provide scientific understanding of phosphorus enrichment behaviour during reduction of oolitic haematite ores. This will in turn boost the utilisation of high phosphorus-containing oolitic haematite ores. (Authors.)