Leaching of Low- Grade Nickel Ores by Fungi Metabolic Acids

This study was designed to investigate the nature of nickel and cobalt dissolution from limonite and weathered saprolite ores. Chemical leaching was conducted using 1 to 3M of citric, lactic and malic acids. These tests aimed to mimic metal dissolution achieved using heterotrophic or fungi organism and their corresponding metabolic products. The results in this study was able to demonstrate the effect of secondary reaction or adsorption, pulp density and the potential hampering effect of acid neutralizing minerals and acid activity or strength on metal dissolution. Nickel and cobalt dissolution were also found to be dependent on the nature of the host minerals and amenability of these gangue minerals to dehydroxylate as a result of acid attack

Adsorption of Metals from Metal-Organic Complexes Derived from Bioleaching of Nickel Laterite Ores

This study aims to establish the potential of an iminodiacetic-based chelating resin (Purolite S930) in recovering Ni and Co from the biological leachate. The adsorption tests were carried out to compare the hydrogen (H) and sodium (Na) forms of resin. The equilibrium adsorption isotherms were determined using metal citrate complexes with concentrations from 15 to 2000 mg/L. Adsorption tests were carried out for a period of 24 hours to attain adsorption equilibrium. The pH of the solution was varied using citric acid with concentrations of 0.01-1.0 M. The adsorption equilibrium data were interpreted using the Langmuir and Freundlich models. Metal elution was carried out using 2M HNO3 solution. The adsorption behaviors of nickel and cobalt citrate complexes were found to follow both Langmuir and Freundlich models. The results suggested that metal uptake were influenced by the hydrolysis of the resin and competition of metal complexes with the citrate anion and hydronium ion (H+). Metal elution was influenced by the interaction or reaction of metal complexes with the resin which included surface complexation

Dye adsorption onto char from bamboo

Experiments have been carried out to prepare char from waste bamboo scaffolding for wastewater treatment. Carbonisation parameters such as temperature, holding time, heating rate and particle size were investigated. When the material was heated to 1173K for 2 h, surface area (SBET-N2) and total pore volume (V-total) were 327 m(2)/g and 0.185 cm(3)/g, respectively. Particle size and heating rate appear less influential to the yield and textural characteristics of the resultant chars. Bamboo char obtained in this study did not show very high adsorption capacities for two acid dyes (Acid Blue 25 and Acid Yellow 117) but exhibited significant uptake of Methylene Blue. The equilibrium data were modelled by three different isotherms, namely, Langmuir, Freundlich and Redlich-Peterson model. Comparing the predicted data using optimised parameters from each model based on the SSE error function, the Redlich-Peterson isotherm appears the `best' model to correlate experimental data. (C) 2010 Elsevier B.V. All rights reserved

Mesoporous activated carbon from waste tyre rubber for dye removal from effluents

The disposal of waste tyre represents a serious concern in environmental management. Owing to the high carbon content of waste tyre rubber, it is feasible to convert waste tyres to a value-added product, i.e. activated carbon, for environmental applications. This study focuses on the effect of different activation conditions (e.g. temperature, holding time and acid treatment) on the porosity of activated carbons produced from tyre rubber. Experimental studies showed that nitric acid treatment to tyre chars is able to remove certain mineral contents such as Ca, K and Na, which affect the reactivity of gas-solid reactions in the subsequent physical activation process (CO2 as activating agent). Those acid-treated carbons developed high surface areas (over 1000 m(2)/g) that were comparable to commercial products. They also posses high mesopore volume up to 0.855 cc/g which has been shown favourable to the adsorption of larger-sized dye molecules. The Redlich-Peterson equilibrium isotherm model yielded the best-fit to experimental data for all three dyes using the non-linear error functions. (C) 2009 Elsevier Inc. All rights reserved

Dye adsorption onto activated carbons from tyre rubber waste using surface coverage analysis

Two types of activated carbons from tyre char (with or without sulphuric acid treatment) were produced via carbon dioxide activation with BET surface areas in the range 59-1118 m(2)/g. Other characterisation tests include micropore and mesopore surface areas and volumes, pH, and elemental compositions, particularly heteroatoms such as nitrogen and sulphur. They were correlated to the adsorption capacity which were in the range of 0.45-0.71 mmol/g (untreated) and 0.62-0.84 mmol/g (acid-treated) for Acid Blue 25. In the case of larger-sized molecules like Acid Yellow 117, capacities were in the range of 0.23-0.42 mmol/g (untreated) and 0.29-0.40 mmol/g (acid-treated). Some tyre carbons exhibit a more superior performance than a microporous, commercial activated carbon (Calgoe (R) F400). By modelling the dye adsorption equilibrium data, the Redlich-Peterson isotherm is adopted as it has the lowest SSE. Based on the surface coverage analysis, a novel molecular orientation modelling of adsorbed dyes has been proposed and correlated with surface area and surface charge. For the acid dyes used in this study, molecules were likely to be adsorbed by the mesopore areas. (C) 2010 Elsevier Inc. All rights reserved

Activated carbons from bamboo scaffolding using acid activation

A series of activated carbons were prepared from bamboo by chemical activation with HCl, HNO3 and H2SO4. Unlike phosphoric acid, these three acids are not commonly used as an activating agent for lignocellulosic materials. The effect of operating variables such as activation temperature, impregnation ratio (the mass ratio between bamboo/acid) and holding time were investigated. The resultant carbons were evaluated for the yield, surface area, pore size distribution, pH, elemental composition and ash. At an impregnation ratio (the mass ratio between bamboo/acid) of 1, activated carbon with BET surface area and micropore volume as high as 553 m(2)/g and 0.239 cc/g was obtained at 1173K using H2SO4 as an activating agent. Lower impregnation ratio and shorter holding time were favourable to the yield and surface area while increasing impregnation ratio enhanced mesoporosity of the carbons. This can be attributed to the transformation of micro- to mesopores in the presence of higher `basic' element contents such as nitrogen and sulphur. (C) 2010 Elsevier B.V. All rights reserved

Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era