Papers by Keyword: Metal Adsorption

Abstract: While bioleaching is a proven technology for the efficient recovery of base metals from sulphide minerals, its sustenance is dependent on the continuous availability of ferric ion, Fe³⁺, in soluble form, in bioleach liquor. However, the solubility of ferric ion is low at higher pH thus resulting in the formation of various types of ferric ion precipitates, which decreases leaching efficiency by trapping the leached metals in solution through an adsorption. The effect of initial solution pH on the surface properties of ferric ion precipitates was investigated with a view to establish a relationship between operational pH and surface charge on precipitate and to relate this to the precipitates metal adsorption properties. Ferric ion precipitates recovered from a typical biooxidation process were characterized by XRD, SEM, PSD and zeta potential. Potassium-hydronium jarosite were the main phases identified by X-ray diffraction (XRD) analyses. The SEM results revealed that the precipitates had smooth surfaces with development of sharp edges on the precipitates formed at high pH. The precipitates formed at higher pH had less positive charge and scavenged more copper ions due to the high electrostatic attraction forces. The results from this study revealed that surface charge on a precipitate can give an indication of its metal adsorption capacity and that in order to prevent metal loss and improve extraction efficiency, solution conditions should be maintained such that the resulting precipitates have high positive surface charge to promote high electrostatic repulsion forces.

Abstract: Emulsion gels, that is, hydrogels containing randomly distributed oil microdroplets, and macroporous hydrogels with randomly distributed, non-interconnected, sphere-like macropores with several micrometers in diameter were prepared by the emulsion-gelation method [1]. This method involves the synthesis of hydrogels in an oil-in-water (O/W) emulsion by free radical copolymerization of a monomer with a cross-linker, followed by the washing (removal) of the dispersed oil as a pore template (porogen). The observations of oil droplets in an emulsion and internal structure of a macroporous hydrogel demonstrate that the oil droplets act as a pore-template. The pore size and porosity can be adjusted by varying the O/W volume ratios and surfactant amounts [2]. These gels are used as a bulk and have excellent diffusional permeability to a solute and solvent. The emulsion-gelation method can yield potentially intelligent gels in which the macropores function as spaces for reaction, separation and storage. Novel emulsion gel adsorbents, that is, polymeric hydrogels containing randomly distributed microdroplets of an organic extractant (an oil-soluble complexing agent), were developed for metal adsorption [3,4]. The emulsion gel containing an organophosphorus extractant and organosulfur extractant successfully adsorbed In (III) and Pd (II) ions, respectively. Novel macroporous polymeric hydrogels were developed to entrap and immobilize lipase as a model enzyme [5]. The lipase immobilized within the macroporous hydrogel successfully catalyzed the hydrolysis of triacetin in a model enzyme reaction without leakage of lipase or loss of activity during repeated use.

Abstract: An attempt was made to study the potential of rice husk as an alternative cheap precursor for activated carbon to remove Ni²⁺ from aqueous solution. Rice husk was treated chemically (with NaOH) and physically (carbonization) to prepare rice husk based activated carbon (RHAC). The textural properties of RHAC, i.e. surface area (255 m²/g) and pore volume (0.17 cm²/g), were determined by N₂ adsorption using Brunauer-Emmett-Teller (BET) surface analyzer. RHAC was also characterized for its morphology and its elemental compositions. The adsorption studies for the removal of Ni²⁺ from aqueous solution were carried out using different dosage of RHAC as adsorbent as a function of varied contact time. The concentration of Ni²⁺ was determined by atomic absorption spectrometer (AAS). The results obtained from adsorption studies indicate good potential of rice husk as a cheap precursor to produce activated carbon for the removal of Ni²⁺ from aqueous solution. The equilibrium data from adsorption studies fitted well the of Langmuir and Freundlich isotherm models.