Chemical torrefaction as an alternative to established thermal technology for stabilisation of sugar cane bagasse as fuel.

Dry and chemical torrefaction of sugar cane bagasse was examined in this study with the aim of stabilising and upgrading the fuel properties of bagasse. Dry torrefaction was conducted at temperatures from 160°C to 300°C under inert conditions, whilst chemical torrefaction incorporated a H2SO4 pre-treatment of bagasse. Chemical torrefaction imparted superior chemical and physical properties inducing morphological transformation and textural development with the potential to address issues in handling, feeding and processing bagasse. It increased the energy density of the chars with maximum HHVmass 21.5 MJ/kg and maximum HHVvolume of 7.4 GJ/m3. Chemically torrefied bagasse demonstrated resistance against microbiological attack for 18 months. These features demonstrate the practical value of chemical torrefaction in advancing the utilisation of bagasse as fuel.

Combustion of thermochemically torrefied sugar cane bagasse.

This study compared the upgrading of sugar bagasse by thermochemical and dry torrefaction methods and their corresponding combustion behavior relative to raw bagasse. The combustion reactivities were examined by non-isothermal thermogravimetric analysis. Thermochemical torrefaction was carried out by chemical pre-treatment of bagasse with acid followed by heating at 160-300°C in nitrogen environment, while dry torrefaction followed the same heating treatment without the chemical pretreatment. The results showed thermochemical torrefaction generated chars with combustion properties that are closer to various ranks of coal, thus making it more suitable for co-firing applications. Thermochemical torrefaction also induced greater densification of bagasse with a 335% rise in bulk density to 340kg/m3, increased HHVmass and HHVvolume, greater charring and aromatization and storage stability. These features demonstrate the potential of thermochemical torrefaction in addressing the practical challenges in using biomass such as bagasse as fuel.

Analysis of acid transport through multi-phase epoxy mortars for wastewater structures.

The characteristics of acid migration through epoxy mortars were examined. Diffusion coefficients of typical sewer bio-metabolised acids: sulphuric, nitric, citric and oxalic acids were determined by gravimetric sorption method and fitted to the multi-phase Jacob-Jones model. Acid permeation was characterised by hindered pore diffusion with the extent being determined by the polarity of the acid and epoxy, and by the microstructure of the epoxy. Epoxy with higher polarity was able to reduce the diffusion coefficients by 49, while dense phases of the coating reduced the diffusion coefficient by 5,100. These results reflect the relative influence of epoxy polarity and microstructure on their performance as protective liners in sewers.

Biogenic acids produced on epoxy linings installed in sewer crown and tidal zones.

In this study the biogenic acids generated by microbes on the surface of Bisphenol A epoxy mortar coupons were investigated for up to 30 months. The epoxy coupons were installed in six sewers in three city locations, Sydney, Melbourne and Perth. Coupons were installed in both the crown and the tidal zones of the sewers to capture the effect of location within the pipe on acid production. The coupons were retrieved approximately every 6 months to provide a dynamic analysis of the biogenic acid production. Our results reveal the colonisation of epoxy mortar by the more aggressive acidophilic bacteria occurred within six months to two years of their installation in the sewer pipes. Biogenic acid generation appear to occur homogeneously from the tidal zone to the crown of the sewer pipes. The reduction in the surface pH of the epoxy lining was supported by the successive growth of microbes beginning with fungi followed be neutrophilic and heterotrophic bacteria and finally by the acidophilic bacteria and the corresponding accumulation of organic and sulphuric acids attributed to these organisms. This study also revealed the potential inhibiting effects on the microbes induced by the accumulation of metabolic products on the epoxy surface. The accumulation of organic acids and H2S coincided with the growth and metabolism inhibition of fungi and acidophilic bacteria. These results provide insights into the microbial interaction and biogenic acids production that contribute to lining degradation and corrosion of concrete in sewer pipes.

Effect of film thickness and filler properties on sulphuric acid permeation in various commercially available epoxy mortar coatings.

The performance of various commercially available epoxy mortar coatings was compared by measuring their sulphuric acid diffusivity. Apparent diffusivities, which were measured gravimetrically, were found to be dependent on coating tortuosity. In composite materials like epoxy mortars, the tortuosity was determined by filler properties and polymer alignment. Tortuosity was found to depend on the filler size, their dispersion, filler aspect ratio and concentration. The order and greater alignment of polymer aggregates, which characterises thinner coatings effects higher tortuosity and thus lower permeabilities. The result is that sulphuric acid diffusivities were observed to increase with coating thickness, which challenges the notion that greater coating thicknesses provide greater protection or environmental barrier. The effect of film thickness and filler properties observed in this study has significant implications to the current selection of coatings and sewer protection.

Design and application of a high-temperature microfurnace for an in situ X-ray diffraction study of phase transformation.

Thermal treatment of mineral ores such as ilmenite can initiate phase transformations that could affect their activation or deactivation, subsequently influencing their ability to dissolve in a leaching agent. Most laboratory-based X-ray diffraction (XRD) studies were carried out ex situ in which realistic diffraction patterns could not be obtained simultaneously with occurring reactions and were time-consuming. The availability of synchrotron-radiation-based XRD not only allows in situ analysis, but significantly shortens the data recording time. The present study details the design of a robust high-temperature microfurnace which allows thermal processing of mineral ore samples and the simultaneous collection of high-resolution synchrotron XRD data. In addition, the application of the manufactured microfurnace for in situ study of phase transformations of ilmenite ore under reducing conditions is demonstrated.

Roles of the textural and surface chemical properties of activated carbon in the adsorption of acid blue dye.

This study has demonstrated the use of empirical modeling in resolving the effects of individual carbon properties on acid blue dye adsorption. Acid blue dye adsorption tests were conducted on activated carbons prepared from bagasse by physical (CO2) and chemical (ZnCl2, MgCl2 and CaCl2) techniques. Empirical models based on the carbon textural (surface area and pore size) properties and the surface chemistry inferred from heteroatom (C,H, N, and S) concentration and carbon surface pH were used to resolve the effects of individual carbon properties on acid blue dye adsorption. This form of analysis was conducted to optimize carbon preparation properties, forming the foundation for tailor-making adsorbents from bagasse suitable for acid dye adsorption. A series of statistical analyses (partial F-tests to establish the parameter significance) measured variants including the mean square error, r2 and adjusted r2, normality, and randomness of residuals, and formed the basis for testing the adequacy of these models. The empirical models suggest that a combination of suitable pore structure and distinct basic surface chemistry generated by sulfur- and nitrogen-based groups, which were also elucidated by Fourier transform infrared spectroscopy, is necessary to promote acid dye adsorption.

Recovery of nickel and cobalt from organic acid complexes: adsorption mechanisms of metal-organic complexes onto aminophosphonate chelating resin.

This study examined the recovery of nickel and cobalt from organic acid complexes using a chelating aminophosphonate Purolite S950 resin. These metal complexes are generated by bioleaching nickel laterite ores, a commercial nickel and cobalt mineral oxide, with heterotrophic organism and their metabolites or organic acid products. Equilibrium adsorption tests were conducted as a function of Ni and Co concentrations (15-2000 mg/L), solution pH (0.01 and 0.1 M acids) and three metabolic complexing agents (citrate, malate and lactate). It was shown that the adsorption of the various Ni- and Co-complexes on Purolite were quite low, 16-18 and 5.4-9 mg/g of resin, respectively, in comparison to the smaller nickel ions and nickel sulfate. This was attributed to the bulky organic ligands which promoted crowding effect or steric hindrance. The adsorption of these complexes was further hampered by the strong affinity of the resin to H+ ions under acidic conditions. Mechanisms of adsorption, as inferred from the fitted empirical Langmuir and Freundlich models, were correlated to the proposed steric hindrance and competitive adsorption effects. Nickel and cobalt elution from the resin were found be effective and were independent of the type of metal complexes and metal concentrations. This study demonstrated the relative challenges involved in recovering nickel and cobalt from bioleaching solutions.

Role of heteroatoms in activated carbon for removal of hexavalent chromium from wastewaters.

Heteroatoms are elements including sulfur, nitrogen, oxygen and hydrogen which are found on the surface of activated carbons. This study investigated the surface modification arising from heteroatoms bonding to carbon aromatic rings within the activated carbon and their corresponding influence on the chromium adsorption process. Activated carbons were prepared from bagasse by physical. Chromium removal capacities of these activated carbons by adsorption and reduction were determined. Models which related the chromium adsorption and reduction capacities of activated carbons to carbon acidity and heteroatom site concentrations were established using multi-variable linear regression method. It was found the individual heteroatoms contributed separately to the basicity of the carbon which in turn determined the mechanism by which chromium was removed from solution. The surface areas of the carbons were also observed to influence the adsorption and reduction of chromium. These understandings provide the fundamental method of optimising chromium removal through suitable control of carbon surface chemistry and textural properties.

Roles of physical and chemical properties of activated carbon in the adsorption of lead ions.

Elucidation of the roles of chemical and physical properties of activated carbons is an important basis for the systematic development of adsorbents with optimal properties specific for certain applications. Such an understanding has challenged most researchers and this has been attributed with the difficulty in decoupling the effect of chemical and physical properties that characterize activated carbons. This study proposed empirical modeling in resolving the effects of individual carbon properties in lead adsorption. A model based on lead adsorption and carbon properties including total surface area, mean pore size and heteroatom concentrations has been shown to adequately describe the lead adsorption onto activated carbons prepared from bagasse. To support this investigation a series of activated carbons were prepared from bagasse by physical and by chemical activation techniques. The surface chemical properties of the carbons were inferred from carbon pH and heteroatom concentrations. The physical characterizations of the carbons included total surface area by the BET technique and mean pore size measured using the Horvath-Kawazoe equation. Adsorption tests were conducted using a low concentration of lead (5 ppm) and the solution pH was maintained at 1.0 to maintain lead speciation to the un-complexed Pb(2+) ion. The adequacy of the proposed empirical models was statistically assessed. This form of analysis was shown to provide valuable information in tailor making adsorbents and selecting appropriate adsorbents for lead adsorption.

Preparation of activated carbon using low temperature carbonisation and physical activation of high ash raw bagasse for acid dye adsorption.

Activated carbons were prepared from bagasse through a low temperature (160 degrees C) chemical carbonisation treatment and gasification with carbon dioxide at 900 degrees C. The merit of low temperature chemical carbonisation in preparing chars for activation was assessed by comparing the physical and chemical properties of activated carbons developed by this technique to conventional methods involving the use of thermal and vacuum pyrolysis of bagasse. In addition, the adsorption properties (acid blue dye) of these bagasse activated carbons were also compared with a commercial activated carbon. The results suggest that despite the high ash content of the precursor, high surface areas (614-1433 m2 g(-1)) and microporous (median pore size from 0.45 to 1.2 nm) activated carbons can be generated through chemical carbonisation and gasification. The micropore area of the activated carbon developed from chars prepared by the low temperature chemical carbonisation provides favourable adsorption sites to acid blue dye (391 mg g(-1) of carbon). The alkalinity of the carbon surface and total surface area were shown to have complementary effects in promoting the adsorption of acid blue dye. Adsorption of the anionic coloured component of the acid dye was shown to be promoted in carbon exhibiting alkaline or positively charged surfaces. This study demonstrates that activated carbons with high acid dye adsorption capacities can be prepared from high ash bagasse based on low temperature chemical carbonisation and gasification.