Mingjun Rao

Stepwise extraction of valuable components from red mud based on reductive roasting with sodium salts

The feasibility of an integrated technological route for comprehensive utilization of red mud was verified in this study. Valuable components in the mud, including Fe2O3, Al2O3 and SiO2 were stepwise extracted by magnetic separation and sulfuric acid leaching from reduced red mud, and meanwhile TiO2 was enriched in the leaching residue. Sodium salts were proved to be favorable for the magnetic separation of metallic iron and the subsequent acid leaching of Al and Si, through facilitating the reduction of iron oxides and the growth of metallic iron grains, together with enhancing the activation of Al and Si components during the roasting process. After reductive roasting in the presence of 6% Na2CO3 and 6% Na2SO4, a magnetic concentrate containing 90.2% iron with iron recovery of 95.0% was achieved from the red mud by magnetic separation. Subsequently, 94.7% Fe, 98.6% Al and 95.9% Si were extracted by dilute sulfuric acid leaching from the upper-stream non-magnetic material, yielding a TiO2-rich material with 37.8% TiO2. Furthermore, value-added products of silica gel and Al(OH)3 were prepared from the leachate by ripening and neutralizing.

Extraction of cobalt from laterite ores by citric acid in presence of ammonium bifluoride

Citric acid was used to selectively extract cobalt from limonite-type laterite ores in the presence of ammonium bifluoride. The results show that ammonium bifluoride enhances the leaching of cobalt by citric acid, and 84.5% cobalt is extracted from a laterite ore containing 0.13% Co when leached at ambient temperature for 2 h with 30 g/L citric acid and 10 g/L ammonium bifluoride. Pyrolusite is reduced by citric acid during leaching, cobalt intergrown with which is liberated and subsequently chelated by the citric acid. The extraction of cobalt is enhanced in the presence of ammonium bifluoride because the matrix of silicate minerals is destroyed by ammonium bifluoride and the adsorbed cobalt is subsequently liberated.

Reductive roasting of nickel laterite ore with sodium sulphate for Fe-Ni production. Part II: Phase transformation and grain growth

ABSTRACT In Part II, the correlation between Fe–Ni grain growth and characteristic fusion temperatures of the Na2SO4–laterite mixtures, and phase transformations of the reduced pellets were investigated. For the mechanism of sodium sulphate, Na+ is able to liberate the hosted nickel and iron within lizardite, while SO42– is the sulphur source for the formation of Fe–FeS eutectic compound which can decrease the characteristic fusion temperatures to promote the growth of ferronickel grains. The mean particle size of ferronickel increased from 7.4 μm to 48.6 μm with the addition of 20 wt% Na2SO4.

Reductive roasting of nickel laterite ore with sodium sulfate for Fe-Ni production. Part I: Reduction/sulfidation characteristics

ABSTRACT The selective reduction of nickel and adequate growth of ferronickel grains are imperative for efficient preparation of ferronickel from nickeliferous laterite ore via the process of direct reduction followed by magnetic separation. In Part I, reduction/sulfidation behaviors of a saprolitic laterite ore in the presence of sodium sulfate were investigated, with an emphasis on thermodynamic analysis, selective reduction/sulfidation ratios and kinetics. To separate the interactions between Ni and Fe, chemical titration analysis was adopted to determine the contents of various Ni and Fe species in the roasted pellets, and a modified equation to assay metallic iron content was proposed.

Iron Recovery from Red Mud by Reduction Roasting-Magnetic Separation

This work provided an effective method for comprehensive utilization of red mud, which mainly focused on the first step of recovering iron from a high iron content red mud by reduction roasting-magnetic separation. During the reduction, iron oxides were reduced to metallic iron with the aid of sodium sulfate and sodium carbonate. Effects of the dosages of sodium sulfate and sodium carbonate, roasting temperature and roasting time on the metallization ratio of iron of roasted product, total iron grade and iron recovery of magnetic concentrate were primarily investigated. In the presence of 6% Na2SO4, 6% Na2CO3 and optimal reduction roasting-magnetic separation conditions: roasting temperature of 1050 °C, roasting time of 60 min, magnetic separation feed fineness of 90% passing 74 urn and magnetic field intensity of 0.1 T, a magnetic concentrate containing 90.12% iron with iron recovery of 94.95% was obtained from a red mud containing 48.23% total iron, 7.71% Al2O3 and 7.69% SiO2.

Porous Materials from Thermally Activated Kaolinite: Preparation, Characterization and Application

In the present study, porous alumina/silica materials were prepared by selective leaching of silicon/aluminum constituents from thermal-activated kaolinite in inorganic acid or alkali liquor. The correlations between the characteristics of the prepared porous materials and the dissolution properties of activated kaolinite were also investigated. The results show that the specific surface area (SSA) of porous alumina/silica increases with silica/alumina dissolution, but without marked change of the BJH pore size. Furthermore, change in pore volume is more dependent on activation temperature. The porous alumina and silica obtained from alkali leaching of kaolinite activated at 1150 °C for 15 min and acid leaching of kaolinite activated at 850 °C for 15 min are mesoporous, with SSAs, BJH pore sizes and pore volumes of 55.8 m2/g and 280.3 m2/g, 6.06 nm and 3.06 nm, 0.1455 mL/g and 0.1945 mL/g, respectively. According to the adsorption tests, porous alumina has superior adsorption capacities for Cu2+, Pb2+ and Cd2+ compared with porous silica and activated carbon. The maximum capacities of porous alumina for Cu2+, Pb2+ and Cd2+ are 134 mg/g, 183 mg/g and 195 mg/g, respectively, at 30 °C.

Preparation of Refractory Materials from Ferronickel Slag

The amount of slag produced from a typical ferronickel smelting process is 4 to 6 times that of the metal product, and handling this slag is a huge challenge to the ferronickel industry. The feasibility of a technological route for preparing refractory materials from a ferronickel slag was verified in this study. Based on the thermodynamics analysis, the effect of the sintering temperature on the properties of refractory material from the slag was studied in the presence of magnesia. The results of thermodynamics calculation showed that the reaction of MgO with SiO2 generated forsterite and enstatite, whereas the reaction between MgO and Fe2O3/Al2O3 produced corresponding magnesia spinels. The experimental results showed that a refractory material with refractoriness of 1580 °C, bulk density of 2.88 g/cm3, compressive strength of 106.9 MPa, and apparent porosity of 5.8% was obtained under the conditions of magnesia addition of 15 wt%, sintering temperature of 1350 °C and sintering time of 3 h. With increasing sintering temperature, the bulk density and the compressive strength of refractory material increased but the apparent porosity decreased, mainly attributed to the formation of the liquid phase which promoted the densification of the refractory material.

Effects of Reductive Roasting with Sodium Salts on Leaching Behavior of Non-ferrous Elements in Bauxite Ore Residue

In our previous study, TiO2 was enriched through stepwise removal of SiO2 and Al2O3 via H3PO4 and NaOH leaching from non-magnetic material, which was derived from reductive roasting of bauxite ore residues with sodium salts followed by magnetic separation. In this research, to elucidate the corresponding mechanism, the effects of reductive roasting with sodium salts on leaching behaviors of non-ferrous elements in bauxite ore residues were further investigated. The logC-pH figures have shown the separation between SiO2 and Al2O3 can be achieved through H3PO4 leaching, and the leaching results proved the difference of leaching ratio between SiO2 and Al2O3 in bauxite ore residues was promoted from 30 to 60% after reductive roasting with sodium salts under the optimal H3PO4 concentration of 1.0 mol/L. TiO2 was found not dissolved after reductive roasting as the leaching ratio changed from 53.9% to be less than 3%, which was due to the insoluble perovskite (CaTiO3) generated in the roasting process. In the NaOH leaching process, the difference between the leaching ratio of Al2O3 and SiO2 in bauxite residue changed from 27.1% to about 60% after reductive roasting under the conditions of maximum Al2O3 extraction ratio with 50.wt% NaOH. The above results have indicated that reductive roasting process with sodium salts was not only favorable to the subsequent separation between SiO2 and Al2O3 as well as the enrichment of TiO2 in H3PO4 leaching process, but also beneficial to extraction of Al2O3 and the separation between Al2O3 and SiO2 in NaOH leaching process.

Utilization CFA-Derived Tobermorite Fiber as Crystallization Revulsive in Autoclaved Concrete Block Production

Coal fly ash (CFA), as a by-product generated from coal fired power stations, is widely used for autoclaved concrete block production. It has been found that the generation of tobermorite is great benefit to the block strength during autoclaving. In this study, the tobermorite fibers synthesized from CFA and lime via the hydrothermal process are used as the revulsive to promote the mechanic strength of the concrete blocks. The results show that tobermorite fibers with 0.01–0.5 μm in diameter and 1–3 μm in length are obtained at 200 °C for 0.2 h. As the addition of prepared tobermorite fibers increases from 0 wt% to 2.0 wt%, the compression strength of concrete block increases from 24.6 to 40.5 MPa, and the compression strength of aerated concrete block produced under the optimized conditions can reach above 7.5 MPa.

Roll-up effect of sulfur dioxide adsorption on zeolites FAU 13X and LTA 5A

AbstractThe roll-up effect occurs as a result of the displacement of SO2 with H2O(g) when sulfur dioxide from humid flue gas is adsorbed by zeolites. It is mainly affected by SiO2/Al2O3 ratio (S/A) of zeolites, despite lack of detailed studies on use of hydrophilic zeolite. In this study, two zeolites of FAU 13X (S/A of 1.77) and LTA 5A (S/A of 1.51) were used to explore their roll-up effects using the breakthrough curve method. It is shown that the zeolite structure significantly influences the roll-up effect. The roll-up effect of FAU 13X is more significant than that of LTA 5A at the same water vapor content. The maximum roll-up ratio (η) for LTA 5A and FAU 13X are, respectively, 1.23 and 2.55 within the water vapor content range of 0.9–2.4%. Moreover, η of FAU 13X tends to decrease more rapidly than that of LTA 5A with increasing temperature or decreasing adsorption gas pressure. The presence of oxygen inhibits the roll-up effect and increases the breakthrough time of SO2. For the acid-modified zeolite, there is a positive correlation between η and concentration of Ca2+ or Na+ on zeolite surface, indicating obvious impact of cations on the roll-up effect.