This study aims to investigate the adsorption of methylene blue (MB) over particulate durian peel waste, which is chemically-activated with hydrogen peroxide. The equilibrium data is well-described by the Freundlich isotherm model, which outlines where the MB adsorption takes place predominantly on multilayers and heterogeneous surfaces of the biosorbent. The Freundlich adsorption constants, KF and n, are 11.06 L/g and 2.94, respectively. Thermodynamic data suggests that the MB adsorption occurs spontaneously and exothermically. The enthalpy and entropy for the MB adsorption are obtained as 10.26 kJ/mol and 0.058 kJ/mol K, respectively, in the temperature range of 303–323 K. Based on the stepwise desorption method, the adsorption of MB is dominated by physical interactions, particularly hydrogen bonding.

Abstract:The establishment of an inexpensive leaching control method to prevent the leaching of trace elements from fly ash is required for the utilization of large-scale fly ash as an embankment material. This study examined the effects of the additives on suppressing As, B, and Se leaching from coal fly ash using Ca(OH) 2 , paper sludge ashes (PS Ash 3, PS Ash 4 and PS Ash 5), and filter cake (FC). PS Ash and FC are waste generated in the papermaking and lime industry processes and contain high levels of calcium. The treated fly ash H (FAH) and the resulting mixtures were subjected to a leaching test as per the Environmental Agency of Japan Notifications No. 13. The results indicate that the leaching concentrations of As, B, and Se could be greatly reduced in FAH with the highest effect given by Ca(OH) 2 , followed by PS Ash 3 and PS Ash 5. Ca(OH) 2 greatly reduced both the leaching concentrations of As, B, and Se by about 91-100%, while PS Ash 3 reduced the As and B leaching concentrations by approximately 89-96% and 83-92%, respectively; and PS Ash 5 reduced the Se leaching concentration by about 87-96%. FC did not have any impact on As and B leaching, but reduced Se leaching by about 58-78%. A reason for the decrease in leaching concentrations of As, B, and Se may be the precipitation with calcium or the formation of ettringite. The presence of leached Ca and Na ions are key factors affecting the decrease of As, B, and Se leaching concentrations from fly ash. The utilization of PS Ash 3 and PS Ash 5 as inexpensive additives is a promising method to control the leaching of As, B, and Se into the environment.

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Abstract:The leaching characteristics of arsenic from six CFA (coal fly ash) samples collected from a large scale power plant in Japan were investigated to evaluate more fully the rate of leaching of arsenic and related factors on determining arsenic leaching from different type of CFAs. The procedure of standard leaching tests according to Environmental Agency of Japan Notifications No. 13 was employed in this work. The results indicate that the leaching fractions of arsenic were low levels below 15%, and it was affected by CaO content in CFA. Leaching test results were compared with solution equilibrium calculation to consider the leaching mechanisms: however, experimental results were significantly lower than the equilibrium calculation results. To elucidate the leaching mechanisms, the leaching rate was investigated by extending the leaching tests for a long-term. The concentration of arsenic in the leachate was increased with time, and equilibrium between the solid phase (ash) and the leaching solution was reached in approximately 120 days. It is found that the constant a has a good relationship with CaO content in CFAs, in which the constant a (indicated leaching rate of arsenic) was decreased with an increase of CaO content in fly ash. Therefore, the value of the rate constant a can be said to be the main factor determining arsenic leaching.

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Doping of Ta5+ into TiO2 replaces Ti4+ to decrease the recombination rate and elongate the electron lifetime due to the formation of shallow electron traps from Ti3+ defects. The elongated electron lifetime increases electron population and photocatalytic activity.