PZ8-3 PZ8-3 Depth (feet) Sand (%) Silt (%) Clay (%) Moisture (%) pH Eh (mV) OC (%) IC (%) a) Including sulfate and arsenate b) Without sulfate and arsenate Equivalent Balance for Major Cations and Anions in Leachate for Column A Conclusions - Column leaching of arsenic is less volume intensive than sequential batch leaching. sequential batch leaching. - Tessier extraction shows that most of the arsenic is either in iron oxide phase or adsorbed in silicon oxide phase, hard to leach. in iron oxide phase or adsorbed in silicon oxide phase, hard to leach. - Equivalent plots are based on electcal neutrality. The ratio of cations and anions is nearly 1, indicating that major cations and anions leaching and anions is nearly 1, indicating that major cations and anions leaching from ash are Ca 2+, CO 3 2-, HCO 3 -, SO 4 2- and HAsO from ash are Ca 2+, CO 3 2-, HCO 3 -, SO 4 2- and HAsO Long term leaching of arsenic is limited by leaching of calcium bicarbonate. calcium bicarbonate. - Arsenic leaches from exchangeable and carbonate phases of the ash. - Calcium leaches mostly as calcium sulfate and calcium bicarbonate. - Arsenic leaches mostly as calcium hydrogen arsenate. - Leaching of arsenic and calcium increases with depth. - Most of the arsenic leaches from silt fraction of ash. - Column leaching results can be applied for other locations in the ash impoundment. impoundment. Molar Balance for Leaching of Calcium in Column and Batch Sequential Leaching based on Calcium Compounds in the Ash CaO, CaSO 4, CaCO 3 and Ca 3 (AsO 4 ) 2. CaO, CaSO 4, CaCO 3 and Ca 3 (AsO 4 ) 2. CaSO 4 = Ca 2+ + SO 4 2- CaSO 4 = Ca 2+ + SO 4 2- CaCO 3 = Ca 2+ + CO 3 2- CaCO 3 + H 2 O = Ca 2+ + HCO OH - CaCO 3 + H 2 O = Ca 2+ + HCO OH - Ca 3 (AsO 4 ) 2 = 3Ca AsO 4 3- Ca 3 (AsO 4 ) 2 + 2H 2 O = 3Ca HAsO OH - Ca 3 (AsO 4 ) 2 + 2H 2 O = 3Ca HAsO OH - CaO + H 2 O = Ca OH - CaO + H 2 O = Ca OH -Compound 25 o C CaSO ×10 -5 Ca(OH) ×10 -6 CaCO ×10 -9 Ca 3 (AsO 4 ) 2 6.8× Leaching of Arsenic per ml of Leachate after 14, 42 and 56 days Solid Phase Analysis of Ash Samples from PZ8-3 Location P Properties of Ash Samples for PZ8-3 Location Research Objectives Determine the leaching of arsenic from alkaline coal fly ash using column leaching. Determine the leaching of arsenic from alkaline coal fly ash using column leaching. Compare the continuous column leaching with batch sequential leaching. Compare the continuous column leaching with batch sequential leaching. Determine the effect of column leaching characteristics with depth for one particular depth, and then apply the results for other depths in the same location in the ash impoundment. Determine the effect of column leaching characteristics with depth for one particular depth, and then apply the results for other depths in the same location in the ash impoundment. Arsenic in Alkaline Coal Fly Ash: Column Leaching versus Batch Sequential Leaching Student: Pratibha Naithani Advisor: Prof. Amid Khodadoust Department of Civil and Materials Engineering University of Illinois at Chicago Cumulative Arsenic Removal PZ8-3 Depth (feet) As (mg/kg) Fe (mg/kg) Ca (mg/kg) Mn (mg/kg) B(mg/kg)ND 24 Arsenic leached with Time SampleAs leached Ca leached (mg/kg)(C/Co)(mg/kg)(C/Co) PZ 8-3 (5-9') PZ 8-3 (15-19') PZ 8-3 (24-32') PZ 8-3 ( ') Leaching of Arsenic and Calcium for PZ8-3 Location with Depth ParametersColumn AColumn B Batch Sequential As leached (mg/kg) As leached (C/Co) Ca leached (mg/kg) Ca leached (C/Co) As / Ca leached As leached / Silt As leached / IC Ca leached / IC Leaching Parameters for Location PZ8-3(24-32’): Comparison of Column and Batch Sequential Leaching Major sources of calcium in ash are: CaO, CaSO 4, CaCO 3 and Ca 3 (AsO 4 ) 2.