I.N. Bhattacharya

Rheological behaviour of nickel laterite suspensions

Abstract Studies have been conducted on rheology of nickel laterite suspension at different temperatures, concentrations, particle sizes and pH for both fines and tailings from a hydrocyclone discharge. Fine laterite slurries exhibit a Bingham plastic behaviour at 20% (w/w) solid concentration and above, while the same behaviour is observed for tailing slurries at >25% (w/w) solid concentration. It is also observed that rheological parameters are affected by both pH and temperature. Both the Bingham viscosity and yield stress are minimum at around pH=7 and the viscosity decrease with temperature is between 2- and 3-fold within the experimental range (20–60°C). Further it is also observed that there is a steep increase in viscosity and yield stress between 45 and 50% (w/w) solid concentration. Correlations have been obtained for predicting both Bingham viscosity and yield stress taking into consideration, a non-dimensional parameter Cw/Cw,max, specific surface area and d50.

Factors controlling precipitation of finer size alumina trihydrate

Abstract The study was undertaken to produce superfine alumina trihydrate (ATH) from Bayer liquor. The specialty grade hydroxides suitable for nonmetallurgical applications should conform to certain qualities such as fineness, purity, brightness, etc. In the present paper, the effects of a number of parameters, such as precipitation, temperature, amount of seed, surface area of seed, precipitation time, soda content of pregnant liquor, addition of aluminium sulfate (modifier), etc., on the particle size of the precipitated ATH were examined. At higher temperatures, the particle size increases, whereas it is reduced at lower temperatures. The seed surface area and seed quantity are found to have marked effects on the particle size of the precipitated ATH. The higher seed specific surface area and the higher seed quantity favour the production of finer-sized particles. The increased soda content in the pregnant liquor also produces finer-sized particles. The most important parameter that influenced the precipitation process with respect to the particle size is the addition of a modifier namely, aluminium sulfate. The particle size is reduced to ∼1 μm even with the addition of a small quantity of aluminium sulfate. It is observed that the formation of finer-sized particles is associated with the degree of rate of nucleation, while the level of supersaturation controls the degree of rate of the nucleation. The seed dissolution in excess soda, available in Bayer liquor, enhances this supersaturation level. When aluminium sulfate is added, the alumina available in the modifier and excess dissolution of the seed due to the addition of a modifier further increases the supersaturation. The seed dissolution, thus, may be considered as a major factor that controls the nucleation rate. Therefore, the mechanism for the fine ATH precipitation from Bayer liquor may be modified to follow the steps: (I) seed dissolution, (II) nucleation, (III) agglomeration, and (IV) growth.

Study on the various factors affecting the quality of precipitated non-metallurgical alumina trihydrate particles

Abstract Processes for production of superfine white alumina trihydroxide (ATH) powders from actual plant Bayer liquor have been developed for use in non-metallurgical applications. The specialty grade hydroxides suitable for non-metallurgical application should conform to certain qualities such as fineness, purity, brightness, etc. The effect of a number of parameters such as precipitation temperature, amount of seed, seed surface area, precipitation time, soda content of pregnant liquor, modifier/additives, etc. on the precipitation of ATH were studied to achieve the required fineness. At higher temperatures, a purer product (with respect to soda) is obtained and particle size is increased, whereas at lower temperatures particle size is reduced and the soda quantity in the product is increased. The effect of seed surface area and seed quantity are found to have marked effects on the productivity and particle size of precipitated ATH. Higher seed specific surface area and higher seed quantity favoured productivity and finer particle size. Increased soda content in the pregnant liquor also enhanced productivity and finer size particles. The single most important parameter that influenced the precipitation process with respect to productivity, particle size and purity is the effect of a modifier, namely aluminium sulfate. ATH productivity is doubled when a modifier is added and the particle size is also reduced to ∼1 μm. An improvement in yield and finer size is also observed when organic additives are used.

Electrodeposition of cobalt from aqueous sulphate solutions in the presence of tetra ethyl ammonium bromide

Abstract The effect of tetra ethyl ammonium bromide (TEAB) as an additive on the structural, morphological characteristics of the cobalt metal produced from aqueous sulphate solutions was investigated. The concentration of TEAB was varied in a range of 1–50 mg/L to evaluate its effect on current efficiency, energy consumption and quality of electrodeposited cobalt metal. Smooth and bright deposits of cobalt were obtained at low concentration of TEAB (10 mg/L) maintaining a current efficiency of 99.6%, with a low energy consumption of 2.38 kW·h/kg. X-ray diffraction studies reveal that (100) plane is the most preferred plane of crystal growth during cobalt electrodeposition. Scanning electron micrographs indicate that smooth and uniform deposit of cobalt is obtained at 10 mg/L beyond which the deposit quality deteriorates. Cyclic voltammetric studies indicate that the presence of TEAB in the electrolytic bath polarizes the cathode and decreases the cathodic current considerably. XPS results confirm the electrodeposition of high pure cobalt with no sign of chemical bonding with TEAB as evident from the FTIR spectra.

Role of hydrazine and hydrogen peroxide in aluminium hydroxide precipitation from sodium aluminate solution

Aluminium hydroxide precipitation from synthetic sodium aluminate solution was studied in the presence of hydrazine or hydrogen peroxide. The addition of low concentration of hydrazine is found to be effective, while higher amount of hydrogen peroxide is required to generate similar effect. XRD data confirm the product phase to be gibbsitic by nature. The scanning electron micrographs (SEM) show that agglomerated products form in the presence of hydrazine while fine discrete particles are produced with hydrogen peroxide. The probable mechanism of precipitation in the presence of hydrazine and hydrogen peroxide is also discussed.

An evaluation of cadmium sorption potential of waste aluminium dross

Abstract The removal of Cd(II) from aqueous solution onto aluminium dross surface was investigated. The influence of pH, contact time, initial metal ion concentration and temperature on the effectiveness of the removal process was studied. The variation of adsorption efficiency with pH indicates that the aluminium dross has residual negative charge on the surface. At low pH, H+ ion gets adsorbed preferentially than Cd(II) ion but at higher pH, Cd(II) ion gets adsorbed in larger numbers. It has been further observed that the adsorption efficiency increases with temperature indicating an increase in kinetic energy of the solute ions or decrease in boundary layer resistance to mass transfer. Kinetic study indicated that in the present work the adsorption process follows mainly pseudo-first-order rate model. The low activation energy (18.3 kJ mol−1) reveals that the process is spontaneous and physical in nature. The value of is negative which further decreases with temperature indicating spontaneity of the ad...

Extraction of copper by leaching of electrostatic precipitator dust and two step removal of arsenic from the leach liquor

The paper deals with the extraction of copper from the deposited material of the liner of the electrostatic precipitator (ESP) of the copper smelter plant. These precipitates of ESP liner (ESP dust) generally contain mixed phases of copper and arsenic. An attempt is made to extract copper from ESP dust, subsequently removing arsenic from the leach liquor. The ESP dust containing paramelaconite (6CuO·Cu2O), α-domeykite (Cu3As), metadomeykite (Cu3As), enargite (Cu3AsS4) and (Cu,Fe) SO4·H2O is not a naturally occurring geological mineral; thus comparatively high acid concentration and temperature are required to break the matrix of this mixed material so as to liberate the content. The leaching efficiency of copper was 97% at 97 °C. The acid concentration of 1.5M and pulp density of 20% was found to be optimum. The removal of arsenic as ferric arsenate was carried out in two stages: increasing the pH and precipitation of arsenic by adjusting pH of the solution and by adding ferrous sulfate and hydrogen peroxide. The optimum removal of arsenic was 95% when pH was raised to 2.35 followed by precipitation. The key progression of the process is the recovery of copper from ESP dust as well as removal of arsenic from the leach liquor.

Effect of Tween 80 on electrochemical deposition of cobalt from sulphate solutions

Cobalt is an essential engineering metal among the less abundant metals found in the earth crust with wide range of applications. However due to the scarcity of resources, it is required to produce the metal in a cost effective manner to meet the supply demands. Cobalt is produced by electrodeposition from chloride or sulphate media, the latter being a widely used method. The use of additives in the electrolytic bath during electrodeposition from sulphate solutions can not only solve issues related to current efficiencies, but also result in production of uniform, smooth and bright deposits of the metal. The present work investigates the effect of Tween 80 a non-ionic additive, on the electrodeposition of cobalt. The concentration of the additive Tween 80 was varied over a range of 1–50 mg/L to evaluate the changes in current efficiency, specific energy consumption and quality of electrodeposited cobalt metal. The results indicated that, apart from increasing the current efficiency, the additive produced bright cobalt deposits. A maximum current efficiency of 98.1% was achieved with 20 mg/L Tween 80 in the electrolytic bath. X-ray diffraction studies have revealed that <100> direction is the most preferred orientation of crystal growth during cobalt electrodeposition. However it is shifted to <110> at higher concentrations (50 mg/L) of the additive. Scanning electron micrographs indicate that smooth, compact and uniform deposits of cobalt are obtained at 20 mg/L beyond which there is deterioration in the quality of deposits. Cyclic voltammetric studies indicated polarization of the cathode in the presence of Tween 80. This behaviour was also reflected in the decrease of the rate of electron transfer as evident from exchange current density (i0) values.