Advanced Materials Research Vols. 194-196

Abstract: Fly ash from the municipal solid waste incineration (MSWI) which contains a small amount of heavy metals becomes a threat to human health and other living organisms once emitted into the environment, and has to be treated before disposal. This study focuses on the characteristics of the MSWI fly ash, which involve mineral composing, granularity distributing, specific surface area, pore diameter and pore volume of fly ash, leaching toxicity and chemical species of heavy metals. The experiment results confirm that the fly ashes are mainly composed of sylvite, halite, portlandite and calcium sulfate hydrate, with the the average particle diameter of 15.082 μm and the specific surface area of 4.290 m²/g, and the heavy metals such as Pb, Cu, Cr in the MSWI fly ash are mobile except Hg. This research provides critical information for appropriate MSWI fly ash treatment technology.

Abstract: Pickling sludge is the deposits that generated from the neutralization of pickling waste water with calcium hydroxide in stainless steel pickling process. The main composition of pickling sludge is CaF₂, CaSO₄, Me(OH)_n (M:Fe,Cr,Ni). Solidification /stabilization method is believed to a most economical way to dispose these wastes at present. But the process caused serious compatibilization, it not only took up the scarce land resource, but also wasted nickel, chromium and other resources, in addition, the potential harm of Cr⁶⁺ to the environment still existed. A new thought to recycle the sludge was as following. After drying the sludge, it contained mainly calcium fluoride and metal oxides. The calcium fluoride could replace fluorspar, so the sludge could be used as a raw material for AOD process, where the metal oxides were reduced into the bulk of the metal. This would not only save fluorite, but also could reduce metal oxide of sludge. With more stringent environmental demands and increasingly output of the sludge, the most effective way to reduce the sludge from source is recycling the valuable elements from waste water directly. Solvent extraction combined with vacuum evaporation, spray evaporation and resin absorption coordination were all the effective methods. The resin adsorption process would be another promising method as ion exchange resin was continuously successfully developed. It had been found that treating the waste water with positive resin can remove the metal ions, but how to completely resolve the metal from the resin was still a problem.

Abstract: The traditional manufacturing technique of “liquid phase method” used in a-gypsum producing is with a lot of defects as follows: low quality product caused by the long-time drying, high expense on the drying device and waste of energy in pulverization modification. Our research is aimed at using a continuous manufacturing method to try to fix all the defects that come along with the traditional manufacturing technique. First we heat the gypsum serofluid, causing it to flow, while the dehydration of crystallization water and the formation of hemihydrate gypsum crystal will take place at the same time. Then an instant decompression will make the serofluid blow into a drying tower, causing a vapour explosion, and finishing the two processes of drying and modification at the same time. [1]

Abstract: Much slag occupied the land resources and caused severe damage to the ecological environment. A lot of work has been done on the reclaimation and utilization of slag. The composition, type and characteristics of slag were similar in some way to glass ceramics, which are architectural decoration materials or wearable and corrosion-proof materials with high quality and low price. In this paper, glass ceramics was prepared using hematite slag, which has not been cooled down in order to save energy. The optimum processing condition determined by orthogenesis test to prepare glass ceramics was hematite78.16%, CaF₂3.91%, CaO7.77%, coke10.16%.The smelting temperature is 1550 for 60 min and the crystallization time is 90 min. Microstructure analysis was studied by SEM. The microcrystalline structure was many petals, which was diopside crystal proved by X-ray analysis.

Abstract: Physical modification and chemical modification were used to modify fluorgypsum. Effect of physical modification and chemical modification on the performance of fluorgypsum was studied, and the mechanism of modification was discussed by testing the phase composition and microstructure of modified fluorgypsum, using XRD and SEM. The results showed that fluorgypsum activity was excited effectively by physical modification and chemical modification. Physical modification decreased CaSO₄ grain size and structure regularity, and increased fluorgypsum specific surface area, and the optimum specific surface area was 4600-4900cm²/g. Chemical modification accelerated fluorgypsum hydration and CaSO₄•2H₂O growth, and increased CaSO₄•2H₂O grain size and slenderness ratio. The strength of fluorgypsum was exerted effectively by chemical modification.

Abstract: In this paper, the iron ore tailings that the metallurgy castoff can be recycled were adopted to synthesize forsterite refractory materials, thermal analysis was used to analyze the reaction process of the forsterite. In the lower temperature, the water cirrhosis decomposed reaction in the reaction process of the forsterite was studied during 573～900K. In the higer temperature, the forsterite was formed during mainly 1400～1673K with the solid solution as the binder phase. In accordance with the heatflow change to confirm five characteristic temperature dots to fire the sample, then the SEM and EDAX were used to make sure the thermal analysis results, in this way, the firing technics can be offered.

Abstract: A large amount of urea-formaldehyde (UF) resin waste is generated accompanied with discarded wood-based panels in China. In order to find out a safe and clean technology to recover these wastes, characterization of the nitrogen species released from fast pyrolysis of UF resin was investigated using PY-GC/MS.The results show that nitrogen atom trends to form nitrogen heterocyclic species rather than aliphatic species, especially at high temperature during UF fast pyrolysis. The number of produced species reaches its maximum when temperature was setto the range of 500-600 °C, the proper temperature range for wood fast pyrolysis. During UF resin fast pyrolysis, neither NO, NO₂, N₂O nor their precursors (HCN and HNCO) were observed. These substances were proven to be very harmful to the environment. Most produced nitrogen species havestrong antibacterial activity, andcan greatly enhance the high-valued utilization of bio-oil. Based on these, we concluded that fast pyrolysis is a promising technology to recover the UF resin waste in a safe and clean manner.

Abstract: A restored WC_P/Fe-C composites is manufactured by centrifugal casting method. The microstructure and properties of the restored composites have been investigated by SEM, X-ray diffraction and properties tester. The results show that the distribution of WC_P in the restored composites is even, Size of WC_P is obviously reduced, and their volume fraction attained to about 70 vol.%. The mechanical properties and wear behavior of the restored composites are almost the same as those of the primary composites.

Abstract: Preparation of amorphous silica using Zr-containing silica residue and the properties of the product have been studied. The results show that the separation of amorphous silica from Zr component can be realized using a process flow that pulping, grinding, washing and solid-liquid separation. The main constituent of the product is amorphous state, the content of SiO₂ in the product comes up to 94.3%, the content of ZrO₂ comes up to 7.48%, the grain size is 2-3 μm, the surface area is 494.3 m²/g. The quality of the recovery can meet the requirement of white carbon black standards ISO 5794-1 and HG/T 3061.

Abstract: This study was focused on the recovery of gallium arsenide (GaAs) from semiconductor fabrication sludge. Wet refined methods were applied to recover gallium (Ga) including acid leaching, purified isolation, electrolysis, and coagulation. The result showed that leaching Ga with nitric acid (HNO₃) was more efficient than with sulfuric acid (H₂SO₄). GaAs could be leached with 4 N HNO₃ to obtain 100% Ga⁺ and arsenic (As^—). The pH was adjusted with sodium hydroxide (NaOH). Then, the solution was extracted by di(2-ethylhexyl) phosphoric acid (D₂EHPA) and was back extracted by H₂SO₄. In this way, Ga extraction efficiency was 80%. At the end of the process, electrolysis was applied to recover Ga. The resulting electrolysis efficiency with nickel-copper was only 56% and its purity was 92%. To further increase the recovery of Ga, the leaching solution was adjusted to alkaline solution and was then electrolyzed with platinum-stainless steel. In this way, recovery and purity could be as high as 90% and 94%, respectively. The removal of arsenic was 86% when the leaching solution was added with ferrous sulfate heptahydrate (Fe₂(SO₄)₃‧_xH₂O) to form iron arsenate (AsFeO₄).