Nikhil Dhawan

Kinetics of hydrochloric acid leaching of smithsonite

AbstractThe dissolution kinetics of smithsonite ore in hydrochloric acid solution has been investigated. As such, the effects of particle size (−180 + 150, −250 + 180, −320 + 250, −450 + 320 μm), reaction temperature (25, 30, 35, 40, and 45°C), solid to liquid ratio (25, 50, 100, and 150 g/L) and hydrochloric acid concentration (0.25, 0.5, 1, and 1.5 M) on the dissolution rate of zinc were determined. The experimental data conformed well to the shrinking core model, and the dissolution rate was found to be controlled by surface chemical reaction. From the leaching kinetics analysis it can be demonstrated that hydrochloric acid can easily and readily dissolve zinc present in the smithsonite ore, without any filtration problems. The activation energy of the process was calculated as 59.58 kJ/mol. The order of the reaction with respect to HCl concentration, solid to liquid ratio, and particle size were found to be 0.70, −0.76 and −0.95, respectively. The optimum leaching conditions determined for the smithsonite concentrate in this work were found to be 1.5 M HCl, 45°C, −180 + 150 μm, and 25 g/L solid to liquid (S/L) ratio at 500 rpm, which correspond to more than 95% zinc extraction. The rate of the reaction based on shrinking core model can be expressed by a semi-empirical equation as:

Optimal Recovery of Iron Values from a Low Grade Iron Ore using Reduction Roasting and Magnetic Separation

1 - \left( {1 - X} \right)^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} = k_0 \left[ {HCl} \right]^{0.70} \left( {\frac{S} {L}} \right)^{ - 0.76} r_0^{ - 0.95} \exp \left( {\frac{{ - 59.58}} {{RT}}} \right)t.

Extraction of potash values from pyrophyllite mine waste

A low grade iron ore containing 51.6% Fe, 17.6% SiO2, 4.3% Al2O3, and 3.8% LOI was subjected to reduction roasting followed by low intensity magnetic separation studies. The phase transformation of hematite into magnetite and fayalite due to reduction roasting was investigated using reflected microscope and X-ray diffraction (XRD) techniques. The effects of reduction variables such as reduction time (40−175 min), temperature (750−1000°C), and reductant dosage (3−11%) using activated charcoal were studied. The process was optimized by using central composite rotatable design (CCRD) and response surface methodology. Iron grade from 59−66% with recovery of 9.5−87% was achieved using CCRD experiments. Model equations were developed both for Fe grade and recovery and then optimized within the bounds of experimental conditions. The program predicted 63.3% Fe with 79% recovery with the following optimum conditions: temperature: 950°C, time: 53.04 min, and reductant: 3%.

Understanding the Agglomeration Behavior of Selected Copper Ores Using Statistical Design of Experiments

Crushed ore agglomeration has been used and is considered as a pretreatment step to improve heap leaching performance of complex copper and gold ores. It is well known that proper agglomeration can prevent solution channeling and ponding, improve percolation within the heap and increase metal recovery rates. However, not much is published regarding nickel laterite agglomeration behavior. Agglomerate size distribution and bed permeability are important parameters to evaluate the quality of agglomerates. With proper considerations, electrical conductivity can be used to control the agglomeration conditions. In this study, a nickel laterite ore from Piaui, Brazil was agglomerated and subjected to different tests to evaluate agglomeration conditions. The study included determination of agglomerate size distribution, saturated hydraulic permeability and electrical conductivity response. It has been found that moisture content and acid concentration have opposite effects on the agglomerate size. Also, retention time and drum rotation speed have small effect on agglomerate size. As expected the permeability of the agglomerate bed is strongly correlated to agglomerate size. Electrical conductivity of the agglomerate bed is affected by agglomeration size, moisture content, acid concentration, and external compaction.

Embedding of Carbon Nanotubes on p-Type Silicon for Use in Solar Cells and PV Devices

ABSTRACT A waste sample generated during the mining of pyrophyllite ore is characterized for the extraction of potash values. Mineral liberation analysis (MLA) reveals that the waste material consists of muscovite, K-Feldspar (orthoclase), and pyrophyllite as the major mineral phases. The sample contains 49.5% SiO2, 23.9% Al2O3, 1.8% Fe2O3, and 9.8% K2O as its prime constituents. An effort has been made for the extraction of potash value by physical and chemical beneficiation techniques. Beneficiation studies using magnetic separation, froth flotation, and even chemical leaching with inorganic acids could not extract any appreciable potash values. Finally, a roast leach method using calcium chloride followed by leaching in water has been employed. The process variables such as calcium chloride dosage, roasting time, and temperature are optimized using L9 Taguchi statistical design. It has been possible to achieve about 85% potash values at 900°C, 45 minutes of roasting time and calcium chloride dosage of 75% with respect to the ore. The change in mineral phases in the feed, roast, and leached residue has been characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), which shows the phase conversion into wollastonite and halite potassian.

Recent Advances in the Application of X-ray Computed Tomography in the Analysis of Heap Leaching Systems

The drum agglomeration of two different crushed copper ores (I and II) has been optimized using Taguchis L16 (45) orthogonal array design to determine the optimum conditions for maximizing the average agglomerate size and minimizing the amount of fines. The effects of controllable operating factors including moisture content (ore I: 9.6–11.1%; ore II: 12.8–14%), retention time (2–4 min), drum speed (15–45% critical), drum load (ore I: 13–32%; ore II: 6–24%) and acid concentration (6.5–90 g/L) on the performance of the agglomeration process were studied. For ore I, the maximum average agglomerate size and minimum percent fines (−1 mm) occurred under the conditions: drum load (22.75%), moisture (10.35%), time (4 min), drum speed (30% critical), and acid concentration (41 g/L), whereas for ore II, the same conditions occurred under the drum load (18%), moisture (13%), time (3 min), drum speed (30% critical), and acid concentration (30 g/L). Under the conditions studied for ore I, the most effective parameter for maximizing average agglomerate size and minimizing the amount of fines was found to be drum load. For ore I, time and acid concentration had a measurable effect on maximizing average agglomerate size, whereas moisture had a statistically significant effect on minimizing the amount of fines. For ore II, the most effective parameter for maximizing average agglomerate size and minimizing the amount of fines was found to be acid concentration. Time had a measurable effect on maximizing average agglomerate size, whereas the other variables did not affect the responses significantly for ore II.

Particle damage and exposure analysis in HPGR crushing of selected copper ores for column leaching

Carbon nanotube bundles were precisely grown atop a p-type silicon wafer that had been treated with catalysts to produce geometries that resemble three-dimensional nano-models to extract more power from the sun. The embedded carbon nanotubes bundles on silicon wafer promise more opportunity for each photon of sunlight to interact with resulting solar cell, as a result of increase of surface area available to produce electricity. The paper discusses morphology of grown nanotubes on silicon wafer along with future prospects of Si-CNTs fabricated solar cells.Copyright