Hong Wen Ma

Extraction of Aluminum Hydroxide from Coal Fly Ash by Pre-Desilication and Calcination Methods

Using coal fly ash from one thermal power plant in Ningxia, China as the raw material, aluminum hydroxide powder was successfully extracted by pre-desilication , calcination, dissolution and carbonation precipitation processes. The research results indicated that the mullite, Quartz and glass phase in the coal fly ash could be changed into NaSiO3, NaAlO2 and Na2CaSiO4 after the coal fly ash was treated by desilication and calcination. The SiO2and Al2O3 components in the coal fly ash were mainly separated by dissolving the calcined sample using water. The dissolution rate of Al2O3 from the calcined sample is 91%. The aluminum hydroxide powder extracted from the coal fly ash is bayerite with the particle size of more than 50m. The extraction rate of the aluminum hydroxide from the coal fly ash can be up to 83%.

Preparation of Ultrafine Aluminum Hydroxide from Coal Fly Ash by Alkali Dissolution Process

A new two-step alkali dissolution technique was used to prepare ultrafine aluminum hydroxide from coal fly ash in this study. The first step alkali dissolution was to leach SiO2 from the coal fly ash using sodium hydroxide solution for obtaining the desilicated product with higher Al2O3/SiO2 ratio. The leaching efficiency of SiO2 reached to 40% when the coal fly ash was leached with 8 M sodium hydroxide solution at 95°C for 150 min. The second step alkali dissolution was that the mixtures of the as-desilicated product and white lime were leached with 20 M sodium hydroxide solution at 260°C for 60 min for extracting alumina from the desilicated product. The alumina extraction efficiency was up to 89%. The sodium aluminates solution obtained from the second alkali dissolution was used to synthesize ultrafine Al(OH)3 after treating by lime and NaHCO3 solution respectively. The results of XRD, SEM and chemical analysis revealed that the prepared ultrafine aluminum hydroxide with monoclinic structure was in the form of spherical particles with the average size of 80∼150 nm.

Preparation of Sulphoaluminate-Alite Composite Mineralogical Phase Cement Clinker from High Alumina Fly Ash

Sulphoaluminate-alite cement (SAAC) was successfully prepared from high alumina fly ash. XRD analysis indicated that the optimal mineralogical phase of cement clinker was obtained under condition of MG=1.05, MS =0.95 at 1300oC, and C4A3 S reached the strongest intensity and is 58.73% in the phase of calcined clinckers. SEM observation showed that C4A3 S are well developed into regular diamond/hexagon-shaped crystal with the size of 1~3.5 μm in the clinker. Hydrated clinker exhibited its new formed dominant phases in AFt, C-S-H and Afm. Pillar shaped AFt and sheet shaped AFm coexisted among the colloidal C-S-H substrate. It is demonstrated that the prepared cement shows a compressive strength of 27 MPa (1d), 36 MPa (3d), 49 MPa (28d), and flexural strength of 5.9 MPa (1d), 5.9 MPa (3d), 6.1 MPa (28d), indicated that the hydration product owned a good mechanical strength at early ages and increased steadily in the later stages.

Kinetics of Hydrothermal Decomposition of Potassium Feldspar with Calcium Hydroxide

The aegirine-augite syenite potash ore, taken from Changling, Luonan in Shannxi province, were hydrothermally decomposed over the temperature ranges of 533 K to 563 K using calcium hydroxide as additive. The dissolution ratio of the K2O at different reaction temperature and time was determined. Analysis of the experimental results revealed that the dissolution rate of potash ore satisfies the chemical reaction controlled kinetic equation. The rate constant of hydrothermal reaction at different temperatures was obtained. The activation energy was calculated using the Arrhenius equation. The hydrothermal decomposition mechanism of microcline was proposed.

Convenient Hydrothermal Synthesis of Zeolite a from Potassium-Extracted Residue of Potassium Feldspar

Zeolite A was successfully synthesized via convenient hydrothermal process using potassium-extracted residue of potassium feldspar as a combined source for silica and alumina. Optimization studies on the molar ratios of Na2O/SiO2 and H2O/SiO2, and aging time have been conducted. The results were that pure zeolite A with high crystallinity could be synthesized when the reaction mixture with molar ratios of Na2O/SiO2 and H2O/SiO2 of 2.0 and of 85, respectively, were crystallized at 100°C for 3h. Aging was found to be not prerequisite for the formation of zeolite A in the system. The product was characterized by XRD, FTIR, SEM and calcium exchange capacity. Finally, a comparative study of the zeolite A formation from the potassium-extracted residue and other industrial waste or natural silicate minerals was also carried out.

XPS Studies on ZrO2 Thin Films Deposited on Glass Substrate by Sol-Gel

The chemical composition and the valence state of elements on the surface of ZrO2 thin films deposited on glass substrates have been studied by X-ray photoelectron spectroscopy. Results show that: elements of Na, Mg, Zr, Ca exist in the form of their respective stable state, such as Na2O, MgO, ZrO2, CaO, when heat treated at 500°C for 0.5h; but Si is unstable, and exhibit stoichiometrical disturbances. Results of chemical composition and their content by atom percent of ZrO2 thin films surface reveal that: Si, and Ca diffuse from glass to the thin films in scale; Na diffuses few and Mg collects to the thin films surface. The diffusion of Mg2+ and Ca2+ from glass to ZrO2 thin films is negative diffusion.

Preparation and Characterization of β-SiAlON Ceramics from High Aluminium Fly Ash via Carbothermal Reduction-Nitridation

In this work, β-sialon ceramics were prepared from high-aluminium fly ash via carbothermal reduction-nitridation (CRN) and the physicochemical properties of the materials such as bulk density, apparent porosity, water absorption and flexural strength were also discussed. The results showed that the percentage of β-sialon phase in the product decreases as the temperature increases from 1400°C and the weight of the sintered specimen experienced an increase during 1350°C~1450°C due to the nitridation reactions, and followed by a gradual decrease till 1550°C for the decomposition of β-sialon. It is indicated that the optimum sintering temperature to obtain the highest yield of β-sialon ~93% lies in 1400°C~1450°C. The SEM images revealed that the prepared β-sialon sintered at 1400°C were mainly in shape of elongated prisms, typically ~5μm in length and 0.5~1μm in width. As the temperature increased to 1500°C and above, β-sialon decomposed and the new phases of SiC and AlN were formed at 1550°C as confirmed by XRD.

XPS Studies on Composite TiO2-SiO2 Thin Films Deposited on Metal Substrate by Sol-Gel

Through X-ray photoelectron spectroscopy, by the aid of Ar+ sputtering, chemical composition and the valence state of elements on surface and at depth of TiO2-SiO2 thin films and metal substrates have been studied. Results show that: on surface, elements of Cr, Mn, Ti, Fe exist in the form of their respective stable state, but Si is unstable and exhibits stoichiometrical disturbance when heat treated at 800°C; at depth, after sputtering for 5 minutes and 17 minutes, elements of Cr, Mn, Ti and Ni exist in the form of their respective stable state, but Si and Fe are unstable and exhibit stoichiometrical disturbances; at depth, after sputtering for 57 minutes, all of the Cr, Mn, Ti, Si, Ni and Fe exist in the form of their respective stable state. Results of chemical composition and their content by weight percent of TiO2-SiO2 thin films and metal substrates reveal that: Fe, Cr, and Mn diffuse from metal substrates to the thin films in scale; Ni diffuses few and Si collects to the metal substrate surface

Study on the Macro-Residual Stress of 304 Stainless Steel Coated with TiO2-SiO2 Thin Films by Sol-Gel Process

X-ray diffraction (XRD) method to measure the residual stress in the metal substrate surface layer and the medial oxide layer between thin film and metal substrate was introduced and the sol-gel TiO2-SiO2 thin film was successfully prepared on SUS304 stainless steel substrate by dip-coating process. The macro residual stress existing in metal substrate was analyzed by XRD. It turns out that the compressive stress existing in the metal substrate surface layer decreases with the raising of heat-treated temperature and that the compressive stress of metal substrate surface layer and the tensile stress of the medial oxide layer increase with the increase of the withdrawal speeds of the sol-gel dip-coating. Based on the above study, colored stainless steels of high quality were prepared by sol-gel process for the first time.

Production of Primary Magnesium by the Aluminothermic Reduction of Magnesia Extracted from Dolomite Ore

In this paper, a new process for the production of the primary magnesium is introduced using the dolomite as the raw material. The magnesia and calcium carbonate were prepared from dolomite by acidification. The content of magnesium oxide can reach 98.92% about the magnesia obtained. The magnesia is used to produce primary magnesium by aluminothermic reduction under vacuum condition. The reduction ratio of MgO can be up to 86.14% under the temperature of 1200°C for 5hrs, briquetting pressure of 10MPa and the molar ratio of MgO to Al of 3:2. The content of magnesium is more than 99.90%. The major phases in the briquette residue are corundum and spinel, which can be used as refractory.