Nickel powder precipitation by high-pressure hydrogen reduction

Includes abstract.Includes bibliographical references (leaves 87-91).The effect of impurities on the precipitation behaviour of nickel powder produced by high-pressure hydrogen reduction was investigated in order to determine the factors responsible for the formation of powder with undesirable morphology. In nickel precipitation by hydrogen reduction, two product morphologies have been observed: the spherical, open powder (desirable) and the spherical, closing/closed powder (undesirable). Two major impurities were studied namely; a morphology modifier (a polyacrylic acid derivative) used as an additive and iron which is an inherent impurity

Temperature effect on volatile organic compounds – polydimethylsiloxane Interactions

Temperature dependence of specific retention volumes (og V) of 13 volatile organic compounds (VOCs) of environmental importance between the gas and liquid stationary phase (polydimethysiloxane) (PDMS) were studied using the gas liquid chromatographic technique (GLC). Temperature was varied from 303.15K to 423.15K to allow transport calculations for different seasons. Four PDMS polymers with average molecular weight ranging from 760 to 13 000 were used as solvents. The results of this work confirm that PDMS is well suited for VOCs scrubbing from waste gas streams. Linear plots of log g V against T1 were obtained in all cases permitting predictions and interpolations to temperatures not studied here. Also dependable enthalpies and entropies of solute transfer from the mobile phase to the stationary phase can be calculated. The specific retention volumes reported in this work are in agreement with literature for similar systems. Efforts were taken to ensure the best possible accuracy and trace the possible sources of error. A gas liquid chromatographic system which secured a simple retention mechanism and showed reproducible solute retention over a long period of time was devised

Thermally activated attapulgite as an adsorbent for heavy metals

Thermal activation of attapulgite was investigated. Attapulgite calcined at 6000C was used as an adsorbent for heavy metals in AMD. The effect of solid loading, residence time and adsorption temperature was investigated. Activated attapulgite showed that it could remove more than 99% of Fe, Cu, Co and Ni from AMD. Langmuir isotherm gave the best fit for the adsorption process with maximum adsorption capacities of 8.97, 0.20, 0.32 and 0.32 for Fe, Ni, Cu and Co respectively. The adsorption of Cu and Ni was thermodynamically. The results show that thermally activated attapulgite has potential as an adsorbent for heavy metals from AMD

Atmospheric oxidative and non-oxidative leaching of Ni-Cu matte by acidified ferric chloride solution

The atmospheric leaching of copper-bearing matte by acidic ferric chloride solution was studied at the laboratory scale. The aim was to achieve maximum copper and nickel recovery by investigating the mechanisms of leaching, as well as identifying the effect of temperature, and concentration of ferric chloride and oxygen..

Examination of flotation reagents suitable for nickel concentrator plant

Examination of flotation reagents suitable for a nickel concentrator plant was investigated using nickel sulphide ore. A number of different new reagents were examined for the best suit for the nickel concentrator plant. It was found that more nickel was found on the magnetic particles, which were assumed to be mostly pyrrhotite. A dosage of 50 g/t was found to be a suitable dose for the collector Betacol 380 AC and gave the best results, however, it was found to be expensive. Betacol 380 AB was found to be suitable at a dose of 75% g/t. There was no flotation improvement when depressants were used in conjunction with Betacol 380 AC. An activator (copper sulphate) was found to improve the grade of copper, nickel and iron meaning it activated pentlandite. The ions improved the flotability of sulfides at the normal process pH after grinding in steel mill

Adsorption, kinetic and thermodynamic study of Al, Mn and Fe adsorption with natural attapulgite

Natural attapulgite was utilized as an adsorbent for the removal of Al, Fe and Mn from a mixed metal effluent. Adsorption experiments were carried out by agitation of a fixed amount of attapulgite with a fixed volume of effluent waste stream in a thermostatic shaker for varying times. Attapulgite showed that it was capable of neutralising the acidic waste stream effluent as pH after 3 hour rose from 2 to 7.46. 4% solid loading of attapulgite could remove 85% Mn(II), 90% Al(III) and 100% Fe(III) The experimental data best fit Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and the adsorption mechanism was physisorption. The adsorption process fitted well the pseudo second order kinetics for all metal ions studied. Thermodynamic data showed that Fe(III) and Mn(II) adsorption was thermodynamically spontaneous whilst Al(III) was not thermodynamically spontaneous. The process is endothermic for all metal ions. An increase in temperature resulted in an increase in spontaneity of the adsorption process. An increase in metal concentration resulted in an increase in amount of metal ion adsorbed per unit weight of attapulgite

Leaching kinetics on the removal of phosphorus from waste phosphogypsum by application of shrinking core model

Abstract: This study investigated the removal of phosphorus from waste phosphogypsum by using citric acid as a leaching reagent, evaluated the potential environmental effect of the final product produced and provide recommenda- tions for the application of developed products. A dissolution process was applied and three variables were studies namely, concentration, stirring speed and temperature. The results showed that Phosphorus can suc- cessfully be removed from waste phosphogypsum and the optimum leaching conditions were at the con- centration of 0.5 M and temperature of 40 °C, with no effect observed on varying the stirring speed. Shrinking core model (SCM) was used to determine the best fit for the experimental data. For the pore diffusion model (KD), all correlation coefficients yielded were above 0.9, illustrating a positively linear correlation of KD and leaching behavior for phosphorus. Pore diffusion proved to be the effective rate controlling mechanism for the removal of phosphorus from phosphogypsum. The analysis of moments of particle size distribution (PSD) also showed a reduction in particle size, indicating the dissolution of the solid particles. The application of Toxic Leaching Characteristic Procedure (TLCP) showed low concentrations on the effluent, indicating that the de- veloped product will not contaminate the environment through leaching. The obtained leachate concentrations were within the South African effluent discharge standards. The results also showed that dissolution had a significant contribution on the moments of particle size distribution, in terms of the volume, surface area and particles number. In respect to unconfined compressive strength the products developed can be used for load bearing and as backfill material

Designing of sampling programmes for industrial effluent monitoring

Monitoring of effluent discharges from industrial establishments discharging directly into municipality sewers is one of the major water pollution control activities conducted by municipalities. For largely industrialised municipalities the task can be quite expensive and not effective if sampling programmes are not properly designed. In most cases samples are randomly collected without proper knowledge of the discharge patterns of various industries. As a result the information obtained does not give a good reflection of the quality of effluent being discharged. These problems can be resolved by adapting a statistical approach to the design of sampling programmes. This approach is useful in determining the frequency of sampling, the number of samples needed to estimate the average concentration of target pollution indicator parameters and the magnitude of the uncertainty involved. The benefits and applications of this approach are demonstrated by a case study presented in this paper. It was found that the number of samples and cost of sample analysis can be greatly reduced by the use of systematic instead of random sampling. The statistical approach greatly improves the estimate of monthly means of pollution indicator parameters and is an effective approach for pollution control when coupled with the “polluter pays principle”

Effect of curing temperature and particle size distribution on unconfined compressive strength of raw and treated fly ash-lime modified phosphogypsum waste

Abstract: Voluminous quantity of phosphogypsum waste is generated by phosphoric acid manufacturing industry. Due to limited technologies available to treat the waste and render it useful, this waste is either landfilled or discharged into the sea in a form of slurry. It is critical that the focus shifts from landfilling or disposal into the sea as this result into environment contamination. This study was carried out to determine applications for raw and treated waste phosphogypsum in building and construction and determine the best conditions to produce the final product. Two significant, readily available waste materials namely phosphogypsum and fly ash were used and blended with hydrated lime. Conditions that yielded best strength from a mixture of phosphogypsum-lime-fly ash specimens were at elevated temperatures. The strengths obtained at the temperature of 80 0C were above the permissible strength for building masonry bricks of 3.5 MPa with unconfined compressive strength up to 4.8 MPa. At lower temperature of 40 0C the optimum strength obtained was at the minimal phosphogypsum content of 30%. The optimum strength was achieved at the PG content of 50% for raw PG and 60% for treated phosphogypsum at elevated temperatures. The strengths obtained for the treated phosphogypsum were lower than the minimum permissible load bearing strength due to the non-uniform particles distribution and the presence of impurities and forces of adhesion between citric acid and phosphogypsum. Increasing the curing temperature also reduced the radionuclides initially present in the raw PG without any prior treatment

Measurement of infinite dilution activity coefficients of selected environmentally important volatile organic compounds in polydimethylsiloxane using gas – liquid chromatography

Silicon oil chemically known as polydimethylsiloxane (PDMS) is a high boiling point solvent highly suitable for volatile organic compounds (VOCs) absorption. In order to use PDMS as an absorption solvent for a specific waste gas problem, it is important to determine the infinite dilution activity coefficients of the VOCs to be separated with PDMS. This work reports activity coefficients at infinite dilution of 13 VOCs in polydimethysiloxane determined by the dynamic gas liquid chromatographic technique. The measurements were carried out at various temperatures (i.e, 303.15, 313.15, 323.15., 333.15, 353.15, 373.15, 393.15 and 423.15K). Four PDMS polymers with average molecular weight ranging from 760 to 13 000 were used as solvents. A control column packed by Perkin Elmer to our specifications was used to validate the coating and packing methods. Flow rate dependence of the elution peaks was also investigated by varying it from 10 – 50 ml/min. Precision was improved by reproducing the results using columns with different liquid loading, thus also studying the retention mechanism. The results compare well with the data from previous work using simple headspace and UNIFAC predictions and literature values. The successful comparison gives an indication of the GLC as a rapid, simple and accurate method for studying the thermodynamics of the interaction of a volatile solute with a non volatile solvent