Search Results
Abstract
This article refers to the mineralogical composition and phase transformations of Greek nickeliferous laterites and to their metallurgical behaviour, during preheating and reduction with carbon monoxide. Transformation of goethite to hematite and decomposition of chlorite and serpentine, were identified during preheating. Higher iron metallization was achieved for the ore in which goethite is the main iron mineral and reduction goes up to 95%, whereas it goes up to 50% for the ore in which hematite is the main iron mineral. The higher reducibility, however, seems to be due to the higher specific surface area of the goethitic type of ore.
Abstract
This study presents an evaluation of the decomposition kinetic of low-grade nickeliferous laterite by thermogravimetric analysis. Kinetic parameters were calculated using the Ozawa and the iso-conversional Friedman methods. Simplified kinetics models like those based on the reaction order were also applied for the simulations. Two-dimensional shrinkage models of the reaction interface mechanism were adopted as describing the thermal transformation process from non-isothermal kinetic analysis. The iso-conversional method (model-free kinetics) reveals that the decomposition of low-grade nickeliferous laterite does not follow a single mechanism because the determined activation energies and pre-exponential factor are not constant during the course of the reaction.
Abstract
By means of radiotracers the erosion of a laterite in an industrial fluidized bed calciner was estimated experimentally. Based on experimental data a simplified formula is found which permits calculation of the mass of the dust deriving from erosion when the granulometric composition of the mineral on entry to the calciner is known. Application of this formula in a current industrial case shows that erosion is the main cause of the production of dust. A method for reducing the quantity of dust is proposed.
Abstract
Soil column experiments have been conducted to treat liquid wastes from hospitals containing125I. Three sorbent samples of laterite clay materials with different contents of iron oxides (goethite, 
-FeOOH) and hydroxides were used to sorb anionic iodate. Post-treatment on effluent wastes with sodium hypochlorite (redox reagent) oxidized the iodide to the desirable iodate ion. Effluent pH after treatment ranges between 4.8 to 5.8, which does not vary much from the initial effluent pH of 4.5 before treatment. Results show that 90 to 97% sorption of iodine radionuclides with a decontamination factor ranges between 10–32 was obtained after the first two hours of experiments. Concentration has decreased from the initial 10 Bq/ml to concentration ranges of 0.3 to 0.9 Bq/ml. Batch experiments conducted using different sorbent masses of soils, show that there was a drop in sorption as the mass of soils fell below approximately 0 to 0.25 g. The sorption remains constant with the soil mass above 0.25 g. Another batch experiment using a different concentration shows that the adsorption capacity of the laterite soil was 1.1 
Ci/g. The adsorption is about 96% with a distribution coefficient of 1170.
Abstract
A rapid procedure for determining palladium in catalysts and geoiogical materials is presented. This method involves the use of an241Am (100 mC) source for excitation and employs a PDP-11/05 processor for the data acquisition and analysis by energy-dispersive X-ray fluorescence. The relative standard deviation for 5 independent determinations is less than 3% for 100 seconds of fluorescent time. The calculated and measured values agreed well for both, the prepared standards and the doped Venezuelan laterites. Finally, data on the different sources of error is given including counting time, sample preparation, and total error.
Abstract
We have examined the working diameter of capillary columns with diameter of 5, 7, 10 and 20 mm. These modified capillary columns were carefully filled with local Taiwan laterite (LTL). The porosity and density of these packed columns was 0.51±0.02 g/g and 1.27±0.05 g/cm3, respectively. The diffusion experiments were then carried out in synthetic groundwater with Cs loading of 0.1mM at room temperature. Experimental results have shown that the diffusion profiles of modified capillary columns fit Fick’s second law very well. This result revealed that the working diameter of a capillary column can be expanded to at least to 20 mm without affecting the validity of the derived diffusion coefficients. Among these columns, the ones with 5 mm diameter show the most consistent results of the derived K d , apparent and effective diffusion coefficients. Although the derived distribution and effective diffusion coefficients slightly decrease as the diameter of these columns increases due to the increase of the solid/liquid ratio. These values are still informative of the Cs diffusion in local Taiwan laterite. Moreover, our results clearly demonstrate the potential of using “modified capillary method” to study the diffusion behaviors of concerned radionuclide because columns with large diameter enable the filling with more versatile geological substances.
Abstract
A rapid method for the determination of titanium in geochemical samples using a55Fe radioisotope as the extraction source coupled to a Si(Li) detector and a PDP-11.05 computer is described. The relative standard deviation for a thin sample about 100 mg in weight is less than 4% and it is achieved in a fluorescent time of 100 sec. Data are given for the use of two different internal standards, KBrO3 and K2Cr2O7, the latter being more precise. The values for five international reference standards are in agreement for this method with the reported values. Finally, besides being rapid, no hydrofluoric acid dissolution of fusion is necessary as in atomic absorption and classical methods.
Abstract
The possibility of concentrating Pt, Ir, Au, Ag, Re and some other elements from samples of chromites, sulfide ores, laterites, shales, titanium magnetites, and ultrabasic rocks was studied. A new simple procedure is based on sublimation of elements to be determined in air stream at 1200 °C in the presence of some powdered reagents /e.g., TiO2, Nb2O5, Nb/ to enhance the yield, and on the use of chemical filters /CaO, MgO, TiO2, Al2O3, Nb2O5/ absorbing the interfering volatile elements from the gas phase. Neutron activation and X-ray fluorescence isotopic excitation were used to analyze the obtained concentrates.
Abstract
The comparison of an ambient temperature mercuric iodide spectrometer (HgI2) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI2 spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the NbK
peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela.
Simulating minerals pyroprocessing by thermal analysis
Clinkerisation of cement raw mixes
Abstract
TG and DTA studies on laboratory cement raw mixes and raw dolomite have been extensively reported in the literature. This paper discusses four aspects. (1) Calcination kinetics of raw mix by isothermal TG and calculation of rate constants to derive activation energy by Arrhenius plots. (2) Quantification by TG of minerals in Indian laterites. The amount of goethite appears to influence burnability of raw mix. (3) Determination of practical heat of clinker formation from DTA studies and establishment of enthalpy temperature relationship of raw mix for heat transfer studies in rotary kilns. (4) Prediction of material temperature profile in a dolomite kiln from DTA studies of raw dolomite.
