Role of hydrazine and hydrogen peroxide in aluminium hydroxide precipitation from sodium aluminate solution

Aluminium hydroxide precipitation from synthetic sodium aluminate solution was studied in the presence of hydrazine or hydrogen peroxide. The addition of low concentration of hydrazine is found to be effective, while higher amount of hydrogen peroxide is required to generate similar effect. XRD data confirm the product phase to be gibbsitic by nature. The scanning electron micrographs （SEM） show that agglomerated products form in the presence of hydrazine while fine discrete particles are produced with hydrogen peroxide. The probable mechanism of precipitation in the presence of hydrazine and hydrogen peroxide is also discussed.

Optimization of operation conditions for extracting lithium ions from calcium chloride-type oil field brine

AI（OH）3 was prepared to extract lithium ions from calcium chloride-type oil field brine. The influences of four factors, namely temperature, Al3＋/Li＋ molar ratio, OH-/Al3＋ molar ratio, and contact time between AI（OH）3 and the brine, on the yield of lithium ions were investigated. It is found that their optimal values are 35℃, 4.5, 2.6, and 6 h, respectively. In the course of the experiment, the apparent pH value was observed. The results reveal that the apparent pH value has no remarkable influence on the yield of lithium ions. Meanwhile, the effects of the concentrations of calcium ions and magnesium ions in the brine on lithium recovery were studied. The results indicate that cal- cium ions have minor negative influence on the yield of lithium ions under optimal conditions, and magnesium ions slightly influence the yield of lithium ions.

Development of high volume rice husk ash alumino silicate composites

The development of high volume rice husk ash （RHA） alumino silicate composites （ASC） was studied. RHA was used as the source of silica and aluminium in the ASC. The mass ratios of RHA：Al（OH）3 of 70：30 to 99：1 were tested. The results indicate that the obtained ASC mortars are not stable and disintegrate in water. Boric acid was introduced to the mixture to overcome this problem. Stable ASC mortars with high RHA：Al（OH）3 mass ratios of 90：10 to 97.5：2.5 were obtained with the use of boric acid and 115oC curing. The compressive strength of the mortar of 20 MPa was gained. The immersion test indicates that high volume RHA ASC mortars show good resistance in 3vol% H2SO4 solution, but is slightly less durable in 5wt% MgSO4 solution.

Bacterial reduction and release of adsorbed arsenate on Fe(III)-, Al- and coprecipitated Fe(III)/Al-hydroxides

Mobilization of arsenic under anaerobic conditions is of great concern in arsenic contaminated soils and sediments. Bacterial reduction of As（V） and Fe（III） influences the cycling and partitioning of arsenic between solid and aqueous phase. We investigated the impact of bacterially mediated reductions of Fe（III）/Al hydroxides-bound arsenic（V） and iron（III） oxides on arsenic release. Our results suggested that As（V） reduction occurred prior to Fe（III） reduction, and Fe（III） reduction did not enhance the release of arsenic. Instead, Fe（III） hydroxides retained their dissolved concentrations during the experimental process, even though the new iron mineral-magnetite formed. In contrast, the release of reduced As（III） was promoted greatly when aluminum hydroxides was incorporated. Thus, the substitution of aluminum hydroxides may be responsible for the release of arsenic in the contaminated soils and sediments, since aluminum substitution of Fe（III） hydroxides universally occurs under natural conditions.

Additives effects on crystallization and morphology in a novel caustic aluminate solution decomposition process

A novel process of caustic aluminate solution decomposition by alcohol medium was developed by the Institute of Process Engineering,Chinese Academy of Sciences in order to solve the problem of low decomposi-tion ratio in the traditional Bayer seeded hydrolysis process.In this research,effects of additives on the crystallization ratio,secondary particle size and morphol-ogy of aluminum hydroxide in the new process were studied to obtain high-quality products.On the basis of primary selection of additives,an orthogonal design L9(3^(4))was used as a chemometric method to investigate the effects of additives.The studied parameters include the reaction style,quantity of additives,caustic soda concen-tration,as well as the combination manner.The crystal-lization ratios of sodium aluminate solution and crystal size of aluminum hydroxide,determined by ICP-OES,SEM and MLPSA(Malvern Laser Particle Size Analyzer),were used to evaluate the effects of the additives.The results showed that different combination manners could promote agglomeration or dispersion.An additive composed by Tween 80 and PEG 200 could promote agglomeration,while a spot of PEG species had a relatively strong dispersion effect.However,the additives had little effects on the crystallization ratios.According to the Raman spectra result,the added alcohol medium might serve as a kind of solvent.