Arsenic removal from coal by ferric chloride enhanced leaching under ultraviolet irradiation during flue gas desulphurization with coal slurry.

During coal combustion, the harmful element arsenic can be released into environment and cause potential significant harm to human beings. Therefore, it is very important to study the removal of arsenic from coal before combustion. In this work, simulated SO2-containing flue gas was used to leach arsenic from coal in a 1 L UV photoreactor. The effects of FeCl3, ultraviolet (UV), pH and the Cl-/Fe3+ molar ratio on arsenic leaching and SO2 removal were experimentally investigated and the enhancing mechanism was analysed. Experimental results demonstrated that FeCl3 and UV could efficiently increase iron and arsenic leaching percentages and SO2 removal efficiency. UV irradiation could induce the oxidation of most trivalent arsenic. The arsenic leaching percentage was significantly larger than that of iron. Low pH was favourable for iron and arsenic leaching. The optimal Cl-/Fe3+ molar ratio was determined to be 3:1. The introduced ferric chloride could not only increase the concentrations of free radicals and ferric iron oxidants, the chloride ion might also impede the formation of passive coatings, thus increasing the arsenic leaching percentage, intensifying the oxidation of trivalent arsenic and enhancing the removal of SO2.

Biosorption of Direct Fast Scarlet 4BS from aqueous solution using the green-tide-causing marine algae Enteromorpha prolifera.

Enteromorpha prolifera, the marine algae frequently causing green tide in the littoral areas in recent years, was investigated as a feasible biosorbent to remove azo dye Direct Fast Scarlet 4BS (DFS-4BS) from aqueous solution. The FTIR spectra of the acid-treated Enteromorpha prolifera (ATEP) biomass before and after dye sorption were used to identify the main functionalities involved in the biosorption process. Results of batch experiments showed that the adsorption capacity of ATEP was dependent on solution pH, ATEP dosage and temperature. The adsorption kinetics followed the pseudo-second order rate equation, while the adsorption isotherm could be well described by the Langmuir model with maximum sorption capacity of 318.87mg·g-1, demonstrating the excellent performance of ATEP as a biosorbent to remove DFS-4BS from aqueous solution. The negative values of free energy change (ΔG°) and positive value of enthalpy change (ΔH°) confirmed that the sorption of DFS-4BS onto ATEP was spontaneous and endothermic in the temperature range of 303-333K. The isosteric heat of adsorption increased with the increase of surface loading, suggesting that the ATEP biomass had heterogeneous surface and lateral interactions might exist among adsorbed molecules. According to the sorption results and the FTIR spectra, it was deduced that the adsorption mechanism involved hydrogen bonding, electrostatic attraction and bonding, and hydrophobic and van der Waals interaction.

SO2 removal with coal slurry in a double-stirred vessel.

In the coal slurry scrubbing process, SO2 can be removed through both the coal pyrite leaching reaction and the oxidation reactions catalysed by Fe2+/Fe3+ produced in situ. In the present study, experiments of SO2 removal with coal slurry (particle size fraction 65-150 microm) were carried out using a double-stirred vessel to investigate the effects of temperature, coal particle size and pulp density on SO2 absorption rate and on the proportion of SO2 removed through the leaching reaction. Results show that the SO2 absorption rate can be increased by decreasing particle size and increasing pulp density, but it is relatively less affected by temperature. Although decreasing coal particle size and pulp density can increase coal pyrite conversion, the effectiveness is limited and the proportion of SO2 removed through the leaching reaction is little affected. Increasing temperature can evidently increase the proportion, but there also exists the problem of energy expenditure; satisfactory coal pyrite conversion during SO2 removal could not be achieved economically by such measures. In addition, the apparent rate constant has a linear relationship with the reciprocal of the coal particle diameter.

[Sodium-enhanced limestone wet FGD in rotating-stream tray scrubber].

Adding sodium sulfate to limestone slurry can increase SO2 removal efficiency. In this paper, sodium-enhanced limestone flue gas desulfurization(FGD) tests were conducted in rotating-stream tray scrubber. Changes of SO2 removal efficiency and pH value with time were experimentally studied and, at different pH range, the dissolution rates of limestone etc. were analyzed. The effects of plate number on SO2 removal efficiency and pressure drop were investigated at temperature approximated to industrial operating value. The average plate efficiencies were calculated. According to the experimental results, increasing plate number could increase SO2 removal efficiency, but the average plate efficiency decreased. Under the experimental conditions, when the plate number was increased from 1 to 4, the removal efficiency was increased from 25.5% to 48.6% at the liquid-to-gas ratio of 4 L/m3, but the average plate efficiency was decreased from 25.5% to 15.3%. The equation of the relation between the average plate efficiency and plate number was obtained.