Nosa O. Egiebor

Control of pyrite oxidation by phosphate coating

Several techniques are currently being investigated for the treatment and abatement of acid mine drainage (AMD). While some of these methods are directed towards the treatment of the resulting drainage, others are directed towards prevention of acid mine drainage at source. Conventional methods of controlling acid mine drainage have primarily been limited to collecting the drainage and neutralizing with alkaline materials which do not provide a permanent solution to the AMD problem. Since the oxidation of pyrite in acid media is initiated by preferential release of iron ions into solution, the mechanism of pyrite oxidation can be likened to the corrosion of metals, and therefore could potentially be protected by metal phosphating techniques. In this communication, the application of low and high temperature phosphating of pyrite to control its rate of oxidation was investigated. The phosphate coated pyrite was tested in an accelerated oxidation column and in an autoclave. The results show that phosphate coating reduces the rate of pyrite oxidation significantly. Phosphating at higher temperatures appears to produce thicker coatings, but did not improve the oxidation stability of the pyrite by any significant amount.

Activated carbon production from synthetic crude coke

Abstract A two-step pyrolysis and activation process was used to study the production of activated carbon from oil sands coke. Steam was employed as the activating agent at atmospheric pressure and 850°C. The activation of raw coke was compared with the activation of coke treated with a potassium hydroxide catalyst. A high BET surface area of 318 m 2 g −1 was obtained for untreated coke activated for 6 h. The addition of a catalyst increased activation rates but did not result in a higher surface area for the potassium-treated activated coke. Surface area generally increased with activation time but was sensitive to the percentage burnoff. The adsorptive capacities of the activated carbons were significantly higher than that of the raw coke. The untreated activated coke had a higher adsorptive capacity for methylene blue than activated potassium coke. The reverse was true for iodine adsorption.

The effect of ferric ion on the rate of ferrous oxidation by Thiobacillus ferrooxidans

Abstractu2002In this study, the effect of ferric ion and cell concentrations on the oxidation of ferrous ion by T. ferrooxidans was investigated. Ferric ions competitively inhibited ferrous ion oxidation by the bacteria. The inhibitory effect of ferric ion was, however, reduced by increasing cell concentration. The apparent ferric ion inhibition constant did not change with increasing cell concentration. The ferrous ion oxidation kinetics in the absence and presence of ferric ion changes from the standard Michaelis-Menten type at low cell concentrations to pseudo-first-order kinetics at high cell concentration.

Evidence for methane reactivity during coal pyrolysis and liquefaction

Abstract Experiments were conducted to determine whether or not methane (natural gas) is an active hydrogenation gas for pyrolysis and liquefaction of Highvale (Alberta subbituminous) coal. Reactions were done under pressure in methane, hydrogen and argon gases in order to compare the toluene-soluble conversions. Tubing bomb micro-reactors were employed at 450 °C and 19–24 MPa. Tetralin was used as the donor solvent for the liquefaction runs and iron oxide was employed as the catalyst for the catalytic experiments. For comparison, a separate set of studies were conducted with standard samples of Illinois no. 6 bituminous coal under similar reaction conditions. The toluene soluble products were analysed by 1 H n.m.r., g.c. and elemental analysis and the gases by g.c. The data for both coals show that under pyrolysis and non-catalytic liquefaction conditions, coal conversions to toluene soluble products were higher for the runs with hydrogen gas than the corresponding methane runs. However, coal conversions under methane gas pressures were higher than those observed in the runs under inert gas (argon) atmospheres, indicating some hydrogenation activity for methane. In the catalytic runs, methane conversions of Highvale coal were consistently higher than the hydrogen conversions while conversions of Illinois no. 6 coal were equivalent. The 1 H n.m.r. analysis of the liquid products from both coals showed that the compositions of the oils observed in the hydrogen and methane runs are similar. G.c. analysis of the liquid products showed alkylation of the donor solvent in the presence of methane to give methyl and dimethyl products.

13C-NMR characterization of organic residues on spent hydroprocessing, hydrocracking and demetallization catalysts

Abstract The carbonaceous residues on spent commercial catalysts for hydrogen treatment of refinery process streams were analyzed by solid-state13C cross-polarization magic angle spinning nuclear magnetic resonance. Catalysts analyzed included Ni/Mo on alumina catalysts from hydroprocessing of coker naphtha and gas oil, Co/Mo on alumina bitumen hydrocracking catalysts, Mo and V/Ni demetallization catalysts, and gas oil hydrocracking catalyst. Spent reforming catalyst was also analyzed for comparison. Residual feed oil was removed by solvent extraction with methylene chloride followed by methanol. The amount of aliphatic carbon on the surface of the catalysts ranged from 0 to 50%, depending on the nature of the feed, and the position of the catalyst in the series of hydrotreating reactors. The aromaticity of surface deposits increased with severity for a given feed oil, but showed no trend with the aromatic carbon content with different feed materials.

Suppression of microbial pyrite oxidation by fatty acid amine treatment

Numerous techniques have been investigated in the past for the treatment and control of acid mine drainage (AMD). While some of these techniques are directed towards the treatment of the resulting drainage, others are directed towards the prevention of AMD at-source. The at-source prevention methods have been found to be promising since, if achieved, they can provide permanent solutions to AMD problem. However, though the bacterium, Thiobacillus ferrooxidans plays an important role in the formation of AMD, and is unavoidable in AMD systems, many of the at-source AMD control and prevention techniques have not been evaluated in the presence of this bacterium. In this study, the stability of fatty acid amine (FAA) treated pyrite in the presence of T. ferrooxidans was investigated. The rate limiting reactions during the oxidation of pyrite, in the absence and presence of the bacterium, was also investigated. The FAA treatment reduces the rate of both the chemical and biological oxidation of the pyrite. In the absence of the bacteria, ferrous to ferric ion oxidation is the rate limiting reaction in pyrite oxidation, while in its presence, ferric oxidation of pyrite is the rate limiting reaction.

13C-NMR OF SOLID ORGANIC DEPOSITS ON SPENT HYDROPROCESSING CATALYSTS

Abstract Carbonaceous deposits on four spent hydroprocessing catalysts were studied using carbon-13 NMR spectroscopy with cross polarization/magic angle spinning (CP/MAS) and dipolar-dephasing technique. The spent catalysts were extracted with methylene chloride and methanol before analysis of insoluble organic material. These deposits, which are generally referred to as “coke”, were found to contain a significant proportion of aliphatic and hydroaromatic structures in addition to aromatic compounds. Different feedstocks and operating conditions formed carbonaceous deposits with different aliphatic carbon contents, ranging from a gas oil catalyst with 62% aliphatic carbon to a bitumen catalyst with only 9% aliphatic carbon. Qualitative dipolar-dephasing experiments showed that the amount of methyl carbon on gas oil catalysts was much greater than on catalysts used to treat naphtha or bitumen. This study shows that solid-state NMR spectroscopy can be used to quantitatively investigate the nature of catalys...

Controlling SO2 emissions in the roasting of gold concentrate

Acid pressure oxidation is generally believed to be the most effective pretreatment for refractory sulfide gold ores and concentrates, although it is ineffective for some ores. For such ores and concentrates (usually those containing both carbonaceous and sulfide materials), roasting remains the most effective pretreatment before cyanidation. However, the serious environmental damage that could result from the emission of SO2 and As2O3 makes roasting an unattractive pretreatment step. In an effort to develop a technique having lower SO2 emissions, a lime agglomeration roast (LAR) pretreatment process was investigated. The technique involves the agglomeration of calcium-based SO2 sorbent with the refractory ore or concentrate before roasting. The results of the LAR pretreatment followed by cyanidation indicate that up to 95 percent of the sulfur dioxide can be captured and more than 90 percent gold extraction can be achieved.

CHEMICAL CHARACTERISTICS OF SUPERCRITICAL TOLUENE EXTRACTS FROM TWO TURKISH LIGNITES

ABSTRACT Samples from two major deposits of Turkish lignites were subjected to supercritical toluene extraction at 325°C and 14.1 MPa in an autoclave. The resultant extracts were separated into pre-asphaltene, asphaltene, saturates, aromatics and resin fractions by column chromatography. The fractions were characterized by 1H-NMR, 13C-NMR, IR. and elemental analysis in order to compare the chemical composition of extracis from the two coal samples. The results show that the extracts from the Tungbiiek (T-coal) deposits contain aliphatic constituent which is composed of mostly long chain unbranched alkyl compounds while the extracts from the Soma Mcrkeg (S-coal) deposits contain a significant amount of branched paraffinic compounds. The resin fractions from both samples were found to contain a significant amount of single ring aromatic compounds.

A MULTIVARIATE ANALYSIS OF PROPERTY-REACTIVITY RELATIONSHIP OF COAL DURING SUPERCRITICAL FLUID EXTRACTION

ABSTRACT Eight Canadian coal samples were subjected to supercritical toluene extraction at 653°K and 20 MPa. The relationship between the chemical composition and the reactivity of coal, in terms of conversion to tars and gases were studied using a multivariate analysis method in order to establish the relative importance of the chemical constituents. An empirical model which predicts the conversion of coal with good accuracy was developed. The variation of coal conversion with chemical composition was investigated using a three dimensional response surface methodology. The results show that the hydrogen and sulfur content of coal have the most significant influence on conversion. Increasing amounts of these two chemical constituents in coal leads to an almost linear increase in conversion, whereas higher contents of oxygen, fixed carbon and ash were found to be deleterious to coal conversion.