Leaching of fluoride from biotite mica in soil : implications for fluoride in shallow groundwater

Leaching of F− from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of F− from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of F− is leached from highly weathered biotite, compared to fresh biotite. Results of dissolution experiments confirm that the organic acids in soil promote the leaching of F− from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of F− from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with F− in biotite treated with citric acid suggests that F− readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of F− into the solution. Our studies suggest that in the presence of organic acids F− is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high F− concentrations by this leaching process

Geochemistry of surface sediments in tsunami-affected Sri Lankan lagoons regarding environmental implications

The December 26, 2004 Indian Ocean tsunami was one of the largest in human history, devastating the coastal wetlands of surrounding countries. This study present the chemical analyses of tsunamigenic and pre-tsunami sediments from Hikkaduwa and Hambantota lagoons in southern Sri Lanka, to assess their geochemical composition, their source, and subsequent environmental impacts. Principal component analysis of the tsunami sediments shows that 42% of the total variance is accounted for calcium oxide and Sr. That is, the tsunami deposits are rich in biogenic phases derived from shallow marine sediments. High organic matter contents of the tsunami sediments of up to 80 wt% also support this interpretation. The association of chlorine (<9.4 wt%), brome (<170 mg/kg), arsenic (<17 mg/kg), iron (III) oxide (<12.9 wt%) and sulfur (<7.6 wt%) accounts for 33% of the variance, reflecting higher salinity. This further suggests that the sediments were mainly derived from a marine environment, rather than from non-marine sands and/or soils. Immobile element contents and relations (thorium, scandium and zirconium) suggest that the tsunami sediment source was mostly felsic in composition, with some mafic component, and mixed with predominantly shallow marine shelf or slope sediments. Additional compositional variations in the tsunami sediments in both lagoons may be associated with variations of wave strength along the coast and by the morphology of the continental shelf. Lower elemental abundances in Hambantota lagoon sediments compared to Hikkaduwa equivalents may thus reflect a greater non-marine component in the former, and greater shelf sediment component in the latter

REMOVAL OF AQUEOUS PHOSPHATE AND PHENOL BY ADSORPTION ON CLAYEY PEAT, LATERITE AND RED EARTH

ABSTRACT Batch and column experiments were carried out to study the removal of phosphate and phenol in wastewater using three natural earth materials commonly found in Sri Lanka: peat, laterite and red earth. Solutions of 100 ml of 50 mg/L phosphate and 50 ml of 50 mg/L phenol were placed in Erlenmyer flask together with various masses of adsorbent for batch experiments. The results showed that a dosage of 3.5 g of clayey peat, 5 g of laterite or 6 g of red earth was required to remove 92.8%, 89.8% and 87.6% of phosphate, respectively. A dosage of 3 g of clayey peat was required to remove 95% of phenol. Adsorption isotherm data were interpreted through Langmuir and Freundlich equations. The results show that the Langmuir model best fits the equilibrium data for phosphate and phenol adsorbent systems. A comparative study shows that clayey peat is more effective than laterite or red earth in phosphate removal. Clayey peat can also be used as an efficient adsorbent material to remove phenol from wastewater

Geochemical and isotopic evidences from groundwater and surface water for understanding of natural contamination in chronic kidney disease of unknown etiology (CKDu) endemic zones in Sri Lanka

<p>Chronic kidney disease of unknown etiology (CKDu) is the main health issue in the dry zone of Sri Lanka. Despite many studies carried out, causative factors have not been identified yet clearly. According to the multidisciplinary researches carried out so far, potable water is considered as the main causative factor for CKDu. Hence, the present study was carried out with combined isotopic and chemical methods to understand possible relationships between groundwater; the main drinking water source, and CKDu in four endemic areas in the dry zone. Different water sources were evaluated isotopically (²H, ³H and ¹⁸O) and chemically from 2013 to 2015. Results revealed that prevalence of CKDu is significantly low with the groundwater replenished by surface water inputs. It is significantly high with the groundwater stagnated as well as groundwater recharged from regional flow paths. Thus, the origin, recharge mechanism and flow pattern of groundwater, as well as geological conditions which would be responsible for natural contamination of groundwater appear as the main causative factors for CKDu. Therefore, detailed investigations should be made in order to identify the element(s) in groundwater contributing to CKDu. The study recommends providing drinking water to the affected zones using water sources associated with surface waters.</p

Convenient process to synthesize reduced needle platy graphite silver nanocomposite: a prospective antibiotic against common pathogenic microorganisms in the environment

Metal nanoparticles (NPs) have earned keen interest due to differences in their physical and chemical properties according to their size. In this study, reduced needle platy graphite silver (rNPG/Ag) nanocomposite has been prepared using natural vein graphite by in-situ chemical reduction method. We found an extraordinary behavior of this rNPG/Ag composite as an antimicrobial agent for pathogenic microorganisms in the environment; Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus. Further, above pathogens can build a resistivity against bare silver NPs as well as the rNPG. This is due to the reduction of permeability and enzyme detoxification or efflux of the toxic metal ions. Also, the antibacterial activity of rNPG can be inhibited by poor penetration into the cell as well as the poor dispersion of the material in the medium. On the other hand, the rNPG/Ag composite is used, the Ag nanoparticles embedded with rNPG sheets can enter into the microbial cell through membrane proteins by simple diffusion or endocytosis which inhibits the microbial activity. This penetration of Ag is facilitated by the rNPG sheets as it contributes to the stability and the nano-sized formation of Ag. Our results conduct to develop broad perspective antimicrobial agent using a straightforward and low-cost chemical route

Vein graphite-based counter electrodes for dye-sensitized solar cells

This paper describes the use of ball-milled vein graphite and ball-milled floated graphite counter electrode (CE) materials in dye-sensitized solar cells. The vein graphite used was ball milled, sieved and fraction of particle sizes in the 45-63 pm was used (BMG). Another fraction in the same size range was floated in water to get ball-milled floated graphite (BMFG). Both samples were extensively characterized by electrochemical techniques, Raman spectroscopy and by Total Carbon Analysis. The performance of dye-sensitized solar cells (DSCs) prepared using these CEs were optimized for their adhesion, sintering temperature and thickness. Best performances were obtained for the DSC with CE prepared using graphite:morphol mass ratio of 5:3, sintering temperature of 350 degrees C and the thickness of 250 mu m. Most of the impurities in ball-milled graphite can be removed by the floating technique and the DSC fabricated with ball-milled floated graphite based CE gives 24% better performance than that constructed using just ball-milled graphite based CE. The best conversion efficiency observed is 6.47%. Though this is less than that obtained using Pt CE, it is still very useful in practical applications as per cost considerations. (C) 2017 Elsevier B.V. All rights reserved

Assessing causes of quality deterioration of groundwater in Puttalam, Sri Lanka, using isotope and hydrochemical tools^†

<p>Extensive extraction of groundwater has resulted in deterioration of the groundwater quality in the Puttalam area in the northwestern coastal zone of Sri Lanka. This situation led us to carry out the present comprehensive study based on environmental isotopic (¹⁸O, ²H, ³H) and geochemical evaluation to understand the root cause for water quality deterioration. The isotopic data suggest that the surface water and shallow groundwaters are subjected to intensive evaporation and, as a result, increase in their salinity. Deep groundwater of the area is mostly recharged by direct infiltration of rainwater and at few places by nearby surface water bodies. The salinity increase of deep groundwater depends on the specific hydrogeological zones and would be due to dissolution of salts which are precipitated in soil through the seawater spray over the time, dissolution of minerals in geological matrix and leaching of salts from salterns. The quality of the deep groundwater is relatively good in the granitic gneiss zone and nearby areas outside the sedimentary aquifer. There is no evidence from isotope and hydrogeochemical evaluation for seawater intrusion into groundwater in the Puttalam area.</p