Zhouyang Liu

Adsorption kinetic and equilibrium study for removal of mercuric chloride by CuCl2-impregnated activated carbon sorbent.

The intrinsic adsorption kinetics of mercuric chloride (HgCl2) was studied for raw, 4% and 10% CuCl2-impregnated activated carbon (CuCl2-AC) sorbents in a fixed-bed system. An HgCl2 adsorption kinetic model was developed for the AC sorbents by taking into account the adsorption kinetics, equilibrium, and internal and external mass transfer. The adsorption kinetic constants determined from the comparisons between the simulation and experimental results were 0.2, 0.3, and 0.5m(3)/(gs) for DARCO-HG, 4%(wt), and 10%(wt) CuCl2-AC sorbents, respectively, at 140 °C. CuCl2 loading was found to slightly increase the adsorption kinetic constant or at least not to decrease it. The HgCl2 equilibrium adsorption data based on the Langmuir isotherm show that high CuCl2 loading can result in high binding energy of the HgCl2 adsorption onto the carbon surface. The adsorption equilibrium constant was found to increase by ~10 times when CuCl2 loading varied from 0 to 10%(wt), which led to a decrease in the desorption kinetic constant (k2) by ~10 times and subsequently the desorption rate by ~50 times. Intraparticle pore diffusion considered in the model showed good accuracy, allowing for the determination of intrinsic HgCl2 adsorption kinetics.

Dissolution kinetics of magnesium hydroxide for CO2 separation from coal-fired power plants

The dissolution of magnesium hydroxide in water for the release of magnesium and hydroxyl ions into the solution to maintain suitable alkalinity is a crucial step in the Mg(OH)2-based CO2 absorption process. In this study, the rate of dissolution of Mg(OH)2 was investigated under different operating conditions using a pH stat apparatus. The dissolution process was modeled using a shrinking core model and the overall Mg(OH)2 dissolution process was found to be controlled by the surface chemical reaction of Mg(OH)2 with H(+) ions. Under the chemical reaction control regime, the dissolution of Mg(OH)2 in alkaline conditions was found not to follow a first-order reaction, and the fractional order of reaction was estimated to lie between 0.20 and 0.31. This suggests that the dissolution reaction is a non-elementary reaction, consisting of a sequence of elementary reactions, via most likely forming a surface magnesium complex. The true activation energy value of 76 ± 11 kJ/gmol was found to be almost twice as much as the observed activation energy value of 42 ± 6 kJ/gmol determined at pH 8.6, and was comparable with the previously reported values. The particle sizes predicted from the intrinsic kinetics determined from the model were in good agreement with the experimentally measured particle sizes during the dissolution process.

Removal of nitrogen and phosphorus from municipal wastewater effluent using Chlorella vulgaris and its growth kinetics

ABSTRACTChlorella vulgaris was used for the removal of residual ammonia/ammonium ion (NH3/) and orthophosphate ion () from secondary wastewater effluent collected from a municipal wastewater treatment plant. The uptake rates for nitrogen and phosphorus were studied with different initial algal cell densities and the addition of CO2 gas for pH control and supply of inorganic carbon. Our result showed that typical NH3/ and concentrations could be readily removed within 48 h. It was found that the culture with an initial algal cell density of ∼350 mg/L and CO2 gas supply could significantly enhance both the rates of cell growth and nutrient uptake. The Monod equation well described the algal cell growth under substrate-limiting conditions, and could be used for the design and operation of photobioreactors for potential tertiary wastewater treatment.

Mechanistic and kinetic studies of elemental mercury oxidation over a RuO2/rutile TiO2 catalyst

Mechanistic and kinetic studies of the heterogeneous oxidation of elemental mercury (Hg(0)) vapor by HCl gas over a RuO2/rutile TiO2 catalyst were conducted. It was found that under reaction conditions, chemically adsorbed HCl was dissociated on the catalyst surface, and the formation of a Ru–H bond was observed by in situ Fourier transform infrared spectroscopy (FTIR). The active chlorine species on the surface generated from HCl was found to be responsible for the Hg(0) oxidation. The intensity of the Ru–H IR signal could be used as an indicator of the available surface chlorine. Based on the in situ FTIR and performance results, Hg(0) oxidation over the RuO2/TiO2 catalyst was proposed to follow an Eley–Rideal followed by Langmuir–Hinshelwood mechanism where HCl is an adsorbed species and reacts with gas-phase Hg(0) to form HgCl(ad), then HgCl(ad) reacts with another Cl(ad) to form HgCl2(ad). A steady-state kinetic study was conducted to determine an intrinsic reaction kinetic expression for Hg(0) oxidation over the catalyst under HCl, NH3 and SO2 gases for the first time. The kinetic expression could reasonably predict the Hg(0) oxidation performance under the competitive adsorption of NH3 and SO2 gases.