Eung Ha Cho

The kinetics of gold cyanide adsorption on activated charcoal

Adsorption rates of gold cyanide on activated carbon were determined as a function of temperature, free cyanide concentration and charcoal concentration. The experimental rate data is explained by use of a diffusion controlled model developed by Crank. The adsorption rates were determined to be controlled by pore diffusion with the effective diffusion coefficient having an activation energy of 3.3 kcal/mol. Good agreement between experimental rate data and predicted rate curves by the diffusion model was obtained.

Kinetics and thermodynamics of silver cyanide adsorption on activated charcoal

An investigation has been carried out on the adsorption of silver cyanide from solution onto activated charcoal. The isosteric heats of adsorption and equilibrium constants for adsorption were determined from adsorption isotherms. The isosteric heat and equilibrium adsorption constants were shown to decrease with increasing surface coverage at low surface coverages while at intermediate surface coverages they remain fairly constant. The experimental isotherm data was found to fit the Langmuir adsorption isotherm in this intermediate range of surface coverage. A pore diffusion model was utilized to explain the experimental rate data. The experimental rates were found to be controlled by pore diffusion with the effective diffusivity having an activation energy of 2.6 kcal/mol. Good agreement between experimental rate data and predicted rate curve by the diffusion model was obtained.

Removal of SO2 with oxygen in the presence of Fe(III)

A laboratory study of the aqueous oxidation of SO2 in the presence of Fe(III) and Fe(II) has been conducted. The SO2 concentration was 3930 ppm (3.93 × 10−3 atm or 398 Pa) in a gas stream with nitrogen and oxygen. The oxygen pressure was varied from 0 to 0.203 atmosphere. The initial concentration of Fe(III) ranged from 10−3 to 5-10−3 molar while that of Fe(II) was 5 × 10−3 molar. The temperatures were 298, 309.2, and 317.5 K. The solution pH was 1.83. The oxidation of SO2 is intensive and yields from 90 to 97 pct recovery of incoming SO2 when 5 × 10−3 molar Fe(III) and an oxygen pressure above 0.057 atmosphere are applied at 298 K. The reaction mechanism has been explained by determining the rate constants of the oxidation reactions from a kinetic model. The rate constants show that SO2 is mostly oxidized by oxygen through formation of ferric-sulfite complex and that regeneration of ferric ion is possible under a normal oxygen pressure. The activation energy of the oxidation has been determined and has been found to be 13.5 Kcal/mole.

Leaching studies of chalcopyrite and sphalerite with hypochlorous acid

Laboratory studies have been conducted on the leaching of chalcopyrite and sphalerite with hypochlorous acid. The effects of stirring speed, temperature, pH, and hypochlorous acid concentration on the leaching rates have been determined. In addition, the leaching mechanisms have been resolved by analyzing the concentrations of the reaction products. It has been found that more than 90 pct extraction of both chalcopyrite and sphalerite can be achieved in one hour using less than 0.3 molar hypochlorous acid at room temperature. The primary leach products of chalcopyrite and sphalerite were sulfur and sulfate in the mole ratios of 1 to 1 and 2 to 1, respectively. A mixed kinetic model was applied to explain the leaching rates of chalcopyrite while a diffusion model was applied to explain the leaching rates of sphalerite. The mixed kinetic model involved steady-state diffusion of hypochlorous acid through the sulfur layer by a chemical reaction at the reaction interface. Good agreement between these models and the leaching rates of both minerals was obtained.Laboratory studies have been conducted on the leaching of chalcopyrite and sphalerite with hypochlorous acid. The effects of stirring speed, temperature, pH, and hypochlorous acid concentration on the leaching rates have been determined. In addition, the leaching mechanisms have been resolved by analyzing the concentrations of the reaction products. It has been found that more than 90 pct extraction of both chalcopyrite and sphalerite can be achieved in one hour using less than 0.3 molar hypochlorous acid at room temperature. The primary leach products of chalcopyrite and sphalerite were sulfur and sulfate in the mole ratios of 1 to 1 and 2 to 1, respectively. A mixed kinetic model was applied to explain the leaching rates of chalcopyrite while a diffusion model was applied to explain the leaching rates of sphalerite. The mixed kinetic model involved steady-state diffusion of hypochlorous acid through the sulfur layer by a chemical reaction at the reaction interface. Good agreement between these models and the leaching rates of both minerals was obtained.

A Kinetic study of leaching of coal pyrite with nitric acid

The leaching of coal pyrite with nitric acid has been investigated. The temperature ranged from 313 to 363 K, and the concentration of nitric acid was varied from 0.154 to 1.54 mol/l. A coal sample of 50 grams was leached in a reactor containing 500 ml of solution in an open system. It was observed that the leaching reaction could remove 47 pct of the pyrite sulfur in seven minutes and 88 pct in 30 minutes at 343 K with 1.54 mol/l of nitric acid. The reaction order with respect to hydrogen and nitrate ion activity was found to be first order. The activation energy for the initial stage of the reaction was determined to be 14.7 K cal/mol (61.5 kJ/mol). A mathematical model was developed on the basis of mixed kinetics (reaction zone model) to explain the leaching rates. Good agreement between experimental rate data and predicted rate curves by the developed model was obtained. Ultimate analysis was used to determine the extent of nitration of the leached coal. This nitration was found to be insensitive to the reaction temperature and acidity of the solution.

Coal desulfurization with aqueous chlorine

A laboratory study on the desulfurization of Sewickley seam coal with aqueous chlorine has been conducted. The coal sample was leached in an acid solution in which chlorine gas was bubbled. The parametric experimental conditions were temperature (25 ‡C, 40 ‡C, and 55 ‡C), stirring speed (230, 360, and 500 rpm), and particle size (35 to 48, 65 to 100, and 150 to 200 mesh). It has been shown that aqueous chlorine can leach more than 90 pct of coal pyrite and approximately 40 pct of organic sulfur at room temperature. The leaching rates are considered to be controlled by pore diffusion mechanisms. The leaching rates decrease slightly as the tem-perature increases. The solubility of chlorine gas that decreases as the temperature increases may be the reason for this trend. A pressurized leaching system is proposed for a future study to increase the concentration of aqueous chlorine and thus remove the sulfur more effectively.

Coal oxidation and calcium loading on oxidized coal

Abstract A Pittsburgh No. 8 coal, and two IBC (Illinois Basin Coal) 101 and 112 coals were oxidized in a 2 1 Parr Stirred Bench Top Reactor. The oxidation time was varied up to 5 h; the temperature from 150°C to 225°C, the oxygen pressure from 100 to 600 psi, and coal dosage from 15 to 60 g in 600 ml of distilled water. The oxidation of coal was evaluated by measuring total acidic group formed on the coal surface as well as by measuring adsorption of calcium ion on the oxidized coal from a solution in a separate system. It was found that upon oxidation of coal, acidic groups were formed on the coal surface and were responsible for the adsorption of calcium ion. The oxidation increased with increasing oxygen pressure without much leveling-off effect. However, the oxidation increased sharply with increase in temperature from 150°C to 180°C and then tended to level off above 180°C. The optimum oxidation conditions were determined by considering BTU loss and Ca/S molar ratio where S is the total sulfur in coal. The optimum oxidation conditions of Pittsburgh No. 8 coal were 170°C and 500 psi O 2 with 60 g of coal for 3 h, while those of IBC 112 coal were 150°C and 500 psi O 2 with 60 g of coal for 3 h. Under these conditions, the Ca/S molar ratio reached approximately 1.3 and the BTU loss was less than 20%. This value of Ca/S molar ratio may be high enough to capture sulfur during fluidized combustion and coal gasification. Thus, it is concluded that the present method has the potential to be used in a commercial process for preparation of a feed stock for fluidized-bed combustion and coal gasification.