Browsing by Author "De Silva, R. C. L"

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Effective use of biochar from the fruit of Cerbera manghas (Wel Kaduru) in treatment of aquatic systems polluted by oil spills
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Nishshanka, H. G. D. M.; De Silva, R. C. L
Open oceans, other marine ecosystems, and inland surface waters are vital aquatic habitats that play a key role in maintaining the environmental balance. Pollution of these environments has become a serious concern in recent decades, with oil spills being a critical issue that needs effective remediation methods. Environmental impacts have been examined concerning the decline of mangroves, invertebrates, seabirds, marine mammals, and affects to the microbial communities. Oil spills can be cleaned up using physical, chemical, and biological methods. Skimmers, booms, and adsorbent materials are the main physical barriers and dispersants and solidifiers are the main chemicals used to treat oil spills. Biological treatments involve the use of microorganisms to degrade oil. Among these, the use of natural sorbents which is a physical method has emerged as a significant topic due to their low cost, high availability, biodegradability, ease of application, and buoyancy. Through this research, the potential use of the fruit of Cerbera manghas (Wel Kaduru), as a natural sorbent to cleanup of oil spills was studied. The fruit was selected by considering its availability mainly in the coastal as well as inland areas in Sri Lanka. Uniformly cut pieces of the dried fruit of Cerbera manghas were pyrolyzed (310–400 ℃, 20 min) in a household kiln under limited oxygen conditions to produce biochar. The efficiency of the produced biochar as a natural sorbent to remove oil was studied by varying several parameters: dosage, size, contact time, oil type, oil volume, salinity, and the effect of weathering. Variations were studied by changing a particular parameter at a time and measuring the adsorption capacities. The study examined different volumes of crude, engine, and motor oils, revealing that the maximum adsorption capacities for these oils ranged from 4.96 to 11.16 g oil/g biochar, depending on the oil type. Additionally, varying the dosage of biochar resulted in maximum adsorption capacities between 7.48 and 10.56 g oil/g biochar for each oil type, suggesting that higher biochar dosages lead to increased oil adsorption. Variation of the contact time of interaction of oil types with the biochar led to maximum adsorption capacities within 30‒45 min. Moreover, the amount of oil adsorbed on the sorbent decreased with time. Further, the extent of removal of oils was strongly affected by the size of the sorbent, as expected, suggesting that small sizes are more effective in the oil cleanup process. The oiladsorbed biochar can be subsequently used for energy production, and further, the ash remaining after burning of oil-adsorbed biochar could be used for dye removal. This adsorption process neither fits the Langmuir isotherm model nor the Freundlich model, indicating that the adsorption is a multilayer process and that the adsorbent is hydrophobic. The use of this natural sorbent would be a beneficial and an effective approach to cleanup oil spills in water sources in a practically applicable manner.
Extraction of alumina from kaolin deposits in gem mines of Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Karunarathna, Y. D. T. I.; De Silva, R. C. L
Aluminum oxide, commonly known as alumina, exhibits multiple polymorphic phases. Most of these phases possess high economic value owing to their versatile industrial applications. The γ phase of alumina finds applications in industries as a catalyst, catalyst support, adsorbent, abrasive, and structural composites. Bauxite, the principal ore for alumina, has become scarce due to extensive exploitation. Due to the limited availability of bauxite ores, there is growing interest in the production of alumina from non-bauxite minerals. Kaolin is a promising alternative for alumina production owing to its abundance, low cost, and high alumina content. Kaolinitic clay deposits, esteemed as valuable mineral resources in Sri Lanka, are widely distributed throughout the country. Some of these clay deposits contain up to 35% alumina by weight. Kaolin deposits in the Ratnapura District are often unearthed during gem mining operations. These excavated deposits are frequently disposed of openly on the ground without undergoing any value-addition process. This practice alters the soil condition in the vicinity, as the clay soil blocks the gravitational flow of rainwater. This environmental impact could be mitigated by adding commercial value to these kaolinitic clay deposits. The present study aims to demonstrate the feasibility of extracting alumina from kaolinitic clay found in gem mining sites. Kaolinitic clay samples were collected from a gem mining site in the Ratnapura District. Kaolin was first transformed into metakaolin by calcining at 600 ºC for 2 hours. Then alumina was extracted from the metakaolin via acid leaching using 6 M HCl as the leaching agent. The Aluminum ions were separated from the leaching solution as Al(OH)3 using 5M NaOH as the precipitating agent. The precipitated Al(OH)3 was transformed into alumina by calcining at 600 ºC. Kaolin, calcined kaolin, and extracted alumina samples were characterized using XRD and XRF analysis. XRD analysis confirmed that the collected clay samples were mineralogically kaolinite. XRF analysis revealed that the kaolin samples were primarily composed of 63.63% silica and 29.11% alumina by weight. Accordingly, the silica/alumina ratio in the sample was 2.18. The successful formation of amorphous metakaolin under the selected calcination conditions was confirmed through XRD analysis. The structure of kaolin shields the aluminum ions. The transformation of kaolin into the amorphous metakaolin phase is necessary for the effective leaching of aluminum ions at low temperatures and short retention times. The extracted alumina samples were found to contain 90.3% alumina and 6.64% silica by weight, as determined by XRF analysis. The silica/alumina ratio in the extracted alumina samples was 0.07. The observed reduction in the silica/alumina ratio signifies the efficient removal of silica during the extraction process. The crystalline phase of the extracted alumina was identified as the γ-phase through XRD analysis. Accordingly, γ-phase alumina with a purity exceeding 90% can be synthesized from the kaolinitic clay sourced from the gem mining site.
Sampling and analysis of Microplastics in the coastal area from the Estuary of Kelani River to the Estuary of Mahaoya
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Weerasekara, P. G. Y. W.; De Silva, D. S. M.; De Silva, R. C. L; Amarathunga, A. A. D.
Plastic particles that are less than 5 mm in dimension are referred to as microplastics (MPs). The formation of MPs can occur either by fragmentation of macroplastics (secondary MPs) or the production of micro-sized plastics (primary MPs) for intended applications. MPs have been identified as an emerging threat to the environment. MP pollution in marine environments around the globe is severe, and enough precautions have not been taken so far for its prevention. The focus of this study was to adopt suitable methods to collect and separate MPs from beach sediment and seawater samples and to identify their presence and the type by the optical microscopy and FTIR-ATR spectroscopic techniques, respectively. Therein, the distribution, types and abundance of MPs along the western coast from the Estuary of the Kelani River to the Estuary of Mahaoya in Sri Lanka were investigated while selecting nine sites along a stretch of 42 km (Hendala, Wattala, Uswetakeiyawa, Sarakkuwa, Bopitya, Dungalpitiya, Morawala, Browns beach and Estuary of Mahaoya). Random sampling was employed to collect a minimum of 8 sediment samples from each site within a 100 m area stretch in the intertidal zone of the beach during October and December 2021. Water samples were also collected parallel to the sediments from the ocean surface. A digestion method was tested and validated using KOH and Methanol. Sodium bromide was used as the density separator to extract MPs from sediment samples as an efficient method. The analysis revealed the presence of MPs in different colours (blue coloured fragments, blue and white coloured fibers, and white and yellow pellets and foams). The FTIR analysis revealed that most of the MPs found were thermoplastic polymers of polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) while some are thermosetting polymers of phenol formaldehyde (PF). Amid the 81 water samples analyzed, the mean abundance varied from 161 items/L (in Hendala) to 2 items/L (in Kepungoda and Browns Beach). Among, the 166 sediments samples analyzed, the mean abundance of MPs varied from 656 items/m2 (in Estuary of Mahaoya) to 3 items/m2 (in Dungalpitiya). The MPs found were identified in different shapes as fragments (80.15%), pellets (14.88%), fibers (2.7%) and foams (2.48%). The FTIR analysis revealed that the beach sediments are mainly contaminated with PE (65.27%) and PP (15.28%) while surface seawater is dominated by PE (60.87%) and PP (4.34%).