Geochemical characteristics of coal samples from Sarawak

Rabuyah, Ni (2007) Geochemical characteristics of coal samples from Sarawak. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Physicochemical characteristic and heavy metal compositions of several coal samples collected from Merit Pilla of Kapit Division, Mukah and Balingian of Mukah Division, and Sungai Mas of Bintulu Division, Sarawak were analyzed. The coal samples were analyzed for proximate data, organic chemicals and heavy metals composition. The coal samples were Soxhlet extracted for 12 hours using dichloromethane to obtained geolipids. The geolipids were subsequently fractionated on activated silica gel column chromatography to produce four fractions. The aliphatic and aromatic fractions were analyzed on capillary gas chromatographylflame ionization detector (GCIFID). Aliphatic and polar fractions were also analyzed on gas chromatography/mass spectrometry (GCIMS). Sungai Mas coal posses low ash, moderate volatile substances and high fixed carbon content and thus can be classified as bituminous coal. Other coals with high content of volatile matter, moderate ash, moderate moisture and moderate fixed carbon content can be classified as sub-bituminous coal. The n-alkanes distribution is characterized by the high concentrations of C25-C33 homologues with C27 or C29 as the most dominant nalkane. Normal alkanes in the range of C23-C33 shows low to moderate odd to even carbon number predominance (CPI range: 0.4 - 2.2). Results based on the composition of the aliphatic hydrocarbons and heavy metals can be used to classify the coals studied into two groups: shale and carbonate source rocks. The appearance of gammacerane peak together with low pristane/phytane, low CPI and abundance of cadmium for Merit Pilla, Mukah and Balingian coals are indication of carbonate source rock origin or deposition under hypersaline environment during formation. Whereas, high CPI value (>1) with dominant of C27 and C28 steranes observed for Sungai Mas coal suggested the organic matters were originated from shale source rock. Domination of CI5 and or CI7 n-alkanes over C14, CI6 and CI8 n-alkanes for Merit Pilla, Mukah and Balingian coals showed a mixture of input from terrestrial plants, planktonic algae and bacteria. Bimodal nalkanes distributions for Balingian and Merit Pilla coals supported the contribution of terrestrial plants and algae. Long chain fatty acid methyl ester and strong predominance of the even carbon number of alcohols also support that the organic matters for 'l Balingian and Merit Pilla coals are associated with terrestrial sources. The sequence for the maturity of coal samples based on results from CPI, pristane/phytane and isoprenoidln-alkanes data are Sungai Mas> Merit Pilla> Balingian > Mukah. The CPI value for coal sample at the diagenetic-catagenetic boundary is approximately 1.28, and Sungai Mas coal exceeded this value. Biodegradation were observed for Sungai Mas coal and this observation is in agreement with aromatic data shown by high pyrenelphenanthrene and phenanthrenelflourene ratios together with the occurrence of C26 tetracyclic terpane. Significant amount of unresolved complex mixture (UCM) in the aliphatic fraction also indicated that enhanced biodegradation activity occurred in the Mukah coal. Balingian and Merit Pilla coals were also subjected to biodegradation based on the occurrence of homohopanes peaks. Manganese was the most abundance heavy metals in all coal samples followed by cobalt and zinc. Other elements such as cadmium, copper and lead were detected only in trace amount. The high contents of manganese in Balingian and Merit Pila can be explained by diagenetic remobilization from lower core section under reducing conditions.

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