Four types of layered double hydroxides (LDHs) were synthesized by a co-precipitation method. The ability of various LDHs to remove anionic species including As(III), As(V), B, Cr(VI) and Se(IV) was investigated. Removal tests were performed primarily by a batch operation. The Cr(VI) removal was conducted by both batch and column studies. For the column removal tests, LDH pellets were prepared using a granulator and 5% poly-vinyl alcohol solution as binder. Among the LDHs tested, Mg-Al-NO3− LDH showed the optimal removal of anionic species, and it demonstrated excellent removal of As(V), Se(IV) and Cr(VI) particularly at the low anionic concentrations. The order of anionic removal by the LDHs is as follows; Mg-Al-NO3− LDH > Mg-Al-Cl− LDH >> Mg-Al-SO42− LDH > Mg-Al-CO32− LDH. The selective uptake of anion had the following order; As(V) > Se(IV) > Cr(VI) > As(III) > B. This study has demonstrated the uptake of harmful anions is influenced by the two specific factors, (1) the originally intercalated anions in the LDH, and (2) valency of anionic target species in aqueous solution. Column study also demonstrated that about 350 times Cr(VI) in solution per unit volume of LDH pellet can be removed, though this resulted in minor change in pH of the solution and greater NO3− elution. This study has revealed the ability of LDH to remove harmful anionic species and its practical application in wastewater treatment.
The objective of this study was to investigate the disinfection efficiencies of E. coli and coliforms during the solar disinfection (SODIS) process with the presence of zero-valent iron and/or citric acid. The experimental results from a series of batch experiments showed that a treatment with neither sole UV-A (365 nm wavelength), zero-valent iron, nor citric acid effectively decreased the fraction of viable E. coli and coliforms under the experimental conditions investigated in this study. However, the simultaneous addition of zero-valent iron and citric acid during the UV-A illumination effectively decreased the fraction of viable E. coli and coliforms, meaning the co-existence of these three are required to effectively produce oxidants such as hydroxyl radical and ferryl ion. It was also demonstrated through field experiments that the technology proposed in this study can be easily implemented in our daily life using lemon juice rich in citric acid.
Bis[(N-ethylaminomethyl)-2-pyridine]amino-silica (BEPS) and bis[(N-propylaminomethyl)-2-pyridine]amino-silica (BPPS) as adsorbents have been synthesizing by the sol-gel process. The adsorption experiments were carried out by a bath method. The adsorption ability of palladium(II) on BEPS was higher than that of BPPS whereas adsorption ability of gold(III) on BPPS was higher than that on BEPS. The thermodynamic parameters showed that entropy change of palladium(II) on BEPS was higher than that on BPPS and gold(III) on BPPS was higher than that of BEPS. These indicate that BEPS and BPPS formed high stable chelating complexes with palladium(II) and gold(III), respectively. While the thermodynamic parameters and adsorption rate constants of platinum(IV) on BPPS indicated that the platinum(IV) adsorption on BPPS is due to an electrostatic interaction.
Catalysts are widely used in petroleum refining and chemical industries. Hydrodesulphurization (HDS) catalysts account for about one third of the total worldwide catalyst consumption. Spent HDS catalysts contain rare metals such as molybdenum, vanadium, nickel and cobalt on an alumina carrier. Among secondary resources, spent HDS catalysts are regarded the most important catalysts for recycling these metals due to not only their large amounts and economic values, but also the environmental concerns if disposed off. In most cases, spent catalysts are treated with hydrometallurgical leaching processes such as caustic leaching and acid leaching with roasting as a pre-treatment step. In the alkaline leaching processes, most of the molybdenum and vanadium are selectively leached over aluminum, nickel and cobalt. Vanadium can be separated from molybdenum with a two stage process based on solvent extraction and precipitation stripping. Molybdenum and vanadium are simultaneously extracted with tri-n-octylamine (TOA) at around pH 4 followed by stripping of molybdenum and vanadium with ammonium salt solutions. In the stripping process, vanadium alone is precipitated as ammonium salts of tetraammonium disodium decavanadate decahydrate at pH > 8. In the present study, precipitation method was carried out to recovery of molybdenum from aqueous solutions of ammonium chloride. Molybdenum could be precipitated as tetraammonium octamolybdate pentahydrate with ammonium chloride at the pH below 4 and the pH region of precipitation increased with increase of temperature. And also, the precipitation of molybdenum with barium chloride and calcium chloride was also investigated.