Victor Rudolph

Phosphate removal from wastewater using red mud

Red mud, a waste residue of alumina refinery, has been used to develop effective adsorbents to remove phosphate from aqueous solution. Acid and acid-thermal treatments were employed to treat the raw red mud. The effects of different treatment methods, pH of solution and operating temperature on adsorption have been examined in batch experiments. It was found that all activated red mud samples show higher surface area and total pore volume as well as higher adsorption capacity for phosphate removal. The red mud with HCl treatment shows the highest adsorption capacity among all the red mud samples, giving adsorption capacity of 0.58 mg P/g at pH 5.5 and 40 degrees C. The adsorption capacity of the red mud adsorbents decreases with increase of pH. At pH 2, the red mud with HCl treatment exhibits adsorption of 0.8 mg P/g while the adsorption can be lowered to 0.05 mg P/g at pH 10. However, the adsorption is improved at higher temperature by increasing 25% from 30 to 40 degrees C. The kinetic studies of phosphate adsorption onto red mud indicate that the adsorption mainly follows the parallel first-order kinetics due to the presence of two acidic phosphorus species, H(2)PO(4)(-) and HPO(4)(2-). An analysis of the adsorption data indicates that the Freundlich isotherm provides a better fitting than the Langmuir model.

Graphdiyne: a versatile nanomaterial for electronics and hydrogen purification

We theoretically extend the applications of graphdiyne, an experimentally available one-atom-thin carbon allotrope, to nanoelectronics and superior separation membrane for hydrogen purification on a precise level.

Novel molecular sieve silica (MSS) membranes: characterisation and permeation of single-step and two-step sol-gel membranes

High quality MSS membranes were synthesised by a single-step and two-step catalysed hydrolyses employing tetraethylorthosilicate (TEOS), absolute ethanol (EtOH), I M nitric acid (HNO3) and distilled water (H2O). The Si-29 NMR results showed that the two-step xerogels consistently had more contribution of silanol groups (Q(3) and Q(2)) than the single-step xerogel. According to the fractal theory, high contribution of Q(2) and Q(3) species are responsible for the formation of weakly branched systems leading to low pore volume of microporous dimension. The transport of diffusing gases in these membranes is shown to be activated as the permeance increased with temperature. Albeit the permeance of He for both single-step and two-step membranes are very similar, the two-step membranes permselectivity (ideal separation factor) for He/CO2 (69-319) and He/CH4 (585-958) are one to two orders of magnitude higher than the single-step membranes results of 2-7 and 69, respectively. The two-step membranes have high activation energy for He and H-2 permeance, in excess of 16 kJ mol(-1). The mobility energy for He permeance is three to six-fold higher for the two-step than the single-step membranes. As the mobility energy is higher for small pores than large pores and coupled with the permselectivity results, the two-step catalysed hydrolysis sol-gel process resulted in the formation of pore sizes in the region of 3 Angstrom while the single-step process tended to produce slightly larger pores

The kinetics of NO and N2O reduction over coal chars in fluidised-bed combustion

This paper presents a comprehensive and critical review of the mechanisms and kinetics of NO and N2O reduction reaction with coal chars under fluidised-bed combustion conditions (FBC). The heterogeneous reactions of NO and N2O with char/carbon surface have been well recognised as the most important processes in reducing both NOx and N2O in situ FBC. Compared to NO-carbon reactions in FBC, the reactions of N2O with chars have been relatively less understood and studied. Beginning with the overall reaction schemes for both NO and N2O reduction, the paper extensively discusses the reaction mechanisms including the effects of active surface sites. Generally, NO- and N2O-carbon reactions follow a series of step reactions. However, questions remain concerning the role of adsorbed phases of NO and N2O, and the behaviour of different surface sites. Important kinetics factors such as the rate expressions, kinetics parameters as well as the effects of surface area and pore structure are discussed in detail. The main factors influencing the reduction of NO and N2O in FBC conditions are the chemical and physical properties of chars, and the operating parameters of FBC such as temperature, presence of CO, O-2 and pressure. It is shown that under similar conditions, N2O is more readily reduced on the char surface than NO. Temperature was found to be a very important parameter in both NO and N2O reduction. It is generally agreed that both NO- and N2O-carbon reactions follow first-order reaction kinetics with respect to the NO and N2O concentrations. The kinetic parameters for NO and N2O reduction largely depend on the pore structure of chars. The correlation between the char surface area and the reactivities of NO/N2O-char reactions is considered to be of great importance to the determination of the reaction kinetics. The rate of NO reduction by chars is strongly enhanced by the presence of CO and O-2, but these species may not have significant effects on the rate of N2O reduction. However, the presence of these gases in FBC presents difficulties in the study of kinetics since CO cannot be easily eliminated from the carbon surface. In N2O reduction reactions, ash in chars is found to have significant catalytic effects, which must be accounted for in the kinetic models and data evaluation

Effect of recirculated leachate volume on MSW degradation

Landfilling represents the most economical method for the disposal of municipal solid waste (MSW). After depletion of the limited volume of air available in void spaces of a waste bed, decomposition in a landfill takes place under anaerobic conditions. Anaerobic digestion requires moisture and a lack of water is generally responsible for retarding degradation of MSW in conventional landfills. Furthermore, the moisture that may be present is seldom uniformly distributed. Bioreac tor landfills are being researched as a means to provide a rapid and predictable stabilisation of waste and landfill gas produc tion. This is achieved primarily by control and management of the liquid flow within the landfill.

Degradation of unsorted municipal solid waste by a leach-bed process

In current landfills breakdown of municipal solid waste (MSW) occurs slowly and the landfill leaves a legacy of care, management, monitoring and potential catastrophic failure over several generations. Social concern over these long term issues, with their legislative and economic implementation, increasingly favour practices which promote short stabilisation times and minimise environmental impact. This paper describes experiments carried out on mixed and unsorted municipal solid waste (MSW) in which 75% of the rapidly biodegradable fraction was degraded in about 2 months with an average yield of 0.18 m(3) CH4/kg volatile solids at s.t.p. The experiments served to demonstrate that with proper leachate management very rapid decomposition of waste can be accomplished by taking the waste through a series of controlled degradation stages

Physical properties of bagasse

Bagasse is a by-product of sugar milling and important fuel resource for that industry. It is a fibrous, low density material with a very wide range of particle sizes and high moisture content. It is difficult to characterize properties of bagasse particles in the usual ways (i.e. by particle density, size, drag co-efficient, etc.). These properties are necessary to apply normal design procedures to, for example, pneumatic conveying, fluidization, drying, combustion, etc. In this paper techniques to determine some physical properties of the three major components of bagasse, namely pith, fibre and rind, are demonstrated. Average material properties may then be obtained based on the weight proportions of the components constituting the bagasse.

Mixed matrix membranes incorporated with size-reduced Cu-BTC for improved gas separation†

Metal–organic frameworks (MOFs), with large surface area and selective gas adsorption capability, can be the promising additives in mixed matrix membranes (MMMs) for potential gas separation. In this study, mixed matrix membranes with dispersed Cu-BTC [Cu3(BTC)2] have been fabricated and employed for gas separation. The sonication treatment was adopted to reduce the crystal size of MOFs and improve their affinity to the polymer matrix. The crystal structure, surface area and gas adsorption properties of as-synthesized and sonication-treated Cu-BTC were measured and compared. The morphology of the derived mixed matrix membranes varied with sonication intensity and Cu-BTC particle size, and the elimination of interfacial voids indicated the improvement of the adhesion between Cu-BTC crystals and the polymer matrix. The permeation test revealed that the gas permeance and selectivity of membranes depend on the crystal size of Cu-BTC fillers. Incorporation of the sonicated Cu-BTC results in enhancing both gas permeability and selectivity of the derived mixed matrix membranes. The analysis of permeation and gas sorption results also indicates that MOFs improve both diffusivity and solubility of gas molecules thus enhancing the permeability and selectivity of the membrane.

Segregation potential in binary gas fluidized beds

Some smoothly fluidized binary mixtures exhibit no tendency to segregate under a particular combination of solids and fluid volume fractions. In these cases the equilibrium mixture remains stable, even in the absence of mixing forces. The conditions corresponding to segregation potential free mixtures can be theoretically predicted from the physical properties of the system, and have been validated for liquid fluidized systems. This paper shows that the same approach may be applied to gas fluidized beds of fine particles. Experimental results of different binary mixtures in gas fluidized beds are reported to support the theory.

In situ synthesis of zeolitic imidazolate frameworks/carbon nanotube composites with enhanced CO2 adsorption

A series of ZIF-8 and hydroxyl-functionalized carbon nanotube (CNT) composites were successfully synthesized by the solvothermal method. The obtained ZIF-8/CNT composites were characterized by XRD, SEM, TGA and N2 adsorption at 77 K. The contents of ZIF-8 and CNTs in the composites were calculated from thermal analysis data. CO2 and N2 adsorption at 273 K on the composites was also investigated and compared. The ZIF-8 particles in the composites exhibit similar crystal structures and morphology to those of pure ZIF-8, but display enhanced thermal stability. The surface areas and pore volumes of the ZIF-8/CNT composites are higher than the values calculated for hypothetical physical mixtures, and the synergetic effect between ZIF-8 and CNTs can be proposed. This phenomenon demonstrates that the incorporation of CNTs into ZIF-8 can facilitate the nucleation and crystallization of ZIF-8. As a result, the composites with an optimal CNT content (3.63 wt%) show improved CO2 adsorption capacity and higher relative selectivity for CO2/N2 compared with pure ZIF-8.