Tingzhi Su

Adsorption Characteristics of As(V), Se(IV), and V(V) Onto Activated Alumina: Effects of PH, Surface Loading, and Ionic Strength

Arsenic, selenium, and vanadium are major anionic elements of concern in drinking water. This research investigated the adsorption characteristics of As(V), Se(IV), and V(V) onto a commercial activated alumina (AA) under different pH, surface loading, and ionic strength conditions using batch systems. The results indicated that the adsorption of these elements was significantly affected by pH and the surface loading. However, ionic strength generally did not impact their adsorption, indicating that the electrostatic effect on the adsorption of these elements was relatively not important compared to surface chemical reactions. A speciation-based adsorption model was used to simulate the adsorption of As(V), Se(IV), and V(V) by activated alumina and to determine the adsorption constants of different element species. This model can satisfactorily predict the adsorption of these elements in a broad pH range from 1.5 to 12 and a wide surface loading range from 1.0 to 50 mg/g activated alumina for different sorbent concentrations, using the same set of adsorption constants.

Quantifying effects of pH and surface loading on arsenic adsorption on NanoActive alumina using a speciation-based model.

Arsenic (As) poses a significant water quality problem and challenge for the environmental engineers and scientists throughout the world. Batch tests were carried out in this study to investigate the adsorption of As(V) on NanoActive alumina. The arsenate adsorption envelopes on NanoActive alumina exhibited broad adsorption maxima when the initial As(V) loading was less than a 50 mg g(-1) sorbent. As the initial As(V) loading increased to 50 mg g(-1) sorbent, a distinct adsorption maximum was observed at pH 3.2-4.6. FTIR spectra revealed that only monodentate complexes were formed upon the adsorption of arsenate on NanoActive alumina over the entire pH range and arsenic loading conditions examined in this study. A speciation-based adsorption model was developed to describe arsenate adsorption on NanoActive alumina and it could simulate arsenate adsorption very well in a broad pH range of 1-10, and a wide arsenic loading range of 0.5-50 mg g(-1) adsorbent. Only four adjustable parameters, including three adsorption constants, were included in this model. This model offers a substantial improvement over existing models in accuracy and simplification in quantifying pH and surface loading effects on arsenic adsorption.

Predicting competitive adsorption behavior of major toxic anionic elements onto activated alumina: A speciation-based approach

Toxic anionic elements such as arsenic, selenium, and vanadium often co-exist in groundwater. These elements may impact each other when adsorption methods are used to remove them. In this study, we investigated the competitive adsorption behavior of As(V), Se(IV), and V(V) onto activated alumina under different pH and surface loading conditions. Results indicated that these anionic elements interfered with each other during adsorption. A speciation-based model was developed to quantify the competitive adsorption behavior of these elements. This model could predict the adsorption data well over the pH range of 1.5-12 for various surface loading conditions, using the same set of adsorption constants obtained from single-sorbate systems. This model has great implications in accurately predicting the field capacity of activated alumina under various local water quality conditions when multiple competitive anionic elements are present.

Distribution of Toxic Trace Elements in Soil/sediment in Post-Katrina New Orleans and the Louisiana Delta

This study provided a comprehensive assessment of seven toxic trace elements (As, Pb, V, Cr, Cd, Cu, and Hg) in the soil/sediment of Katrina affected greater New Orleans region 1 month after the recession of flood water. Results indicated significant contamination of As and V and non-significant contamination of Cd, Cr, Cu, Hg and Pb at most sampling sites. Compared to the reported EPA Region 6 soil background inorganic levels, except As, the concentrations of other six elements had greatly increased throughout the studied area; St. Bernard Parish and Plaquemines Parish showed greater contamination than other regions. Comparison between pre- and post-Katrina data in similar areas, and data for surface, shallow, and deep samples indicated that the trace element distribution in post-Katrina New Orleans was not obviously attributed to the flooding. This study suggests that more detailed study of As and V contamination at identified locations is needed.

Modeling batch leaching behavior of arsenic and selenium from bituminous coal fly ashes

Correctly predicting the leaching potential of arsenic (As) and selenium (Se) is critical for assessing the environmental impact of coal fly ash. This study investigated the impacts of several key environmental factors, including pH, leaching time, and ash washing on the batch leaching behavior of As and Se from bituminous coal fly ashes. The experimental results demonstrated that As and Se leaching from fly ash increased beyond the minimal leaching pH ranges. Increasing leaching time increased As leaching but decreased Se leaching in the alkaline pH condition. A speciation-based adsorption model was used to quantify the batch leaching data, and determine the intrinsic leaching parameters including the total batch leachable mass and the adsorption constant of As or Se. The modeling approach was validated by correctly predicting the independent batch leaching data in a broad pH range and a different L/S condition. Experimental and modeling results also demonstrated that ash washing and ash aging (longer leaching time) did not change the adsorption constants of As and Se on the ash surface. However, ash washing could increase the availability of As and Se for leaching.

Toxic Trace Element Assessment for Soils/sediments Deposited During Hurricanes Katrina and Rita from Southern Louisiana, USA: A Sequential Extraction Analysis

Analysis of soil/sediment samples collected in the southern Louisiana, USA, region three weeks after Hurricanes Katrina and Rita passed was performed using sequential extraction procedures to determine the origin, mode of occurrence, biological availability, mobilization, and transport of trace elements in the environment. Five fractions: exchangeable, bound to carbonates, bound to iron (Fe)-manganese (Mn) oxides, bound to organic matter, and residual, were subsequently extracted. The toxic trace elements Pb, As, V, Cr, Cu, and Cd were analyzed in each fraction, together with Fe in 51 soil/sediment samples. Results indicated that Pb and As were at relatively high concentrations in many of the soil/sediment samples. Because the forms in which Pb and As are present tend to be highly mobile under naturally occurring environmental conditions, these two compounds pose an increased health concern.Vanadium and Cr were mostly associated with the crystal line nonmobile residual fraction. A large portion of the Cu was associated with organic matter and residual fraction. Cadmium concentrations were low in all soil/sediment samples analyzed and most of this element tended to be associated with the mobile fractions. An average of 21% of the Fe was found in the Fe-Mn oxide fraction, indicating that a substantial part of the Fe was in an oxidized form. The significance of the overall finding of the present study indicated that the high concentrations and high availabilities of the potentially toxic trace elements As and Pb may impact the environment and human health in southern Louisiana and, in particular, the New Orleans area.