B. R. Hart

Leachability of elements from sub-bituminous coal fly ash from India

Environmental concerns regarding the potential contamination of soil, surface and ground water due to the presence of soluble metal species in the ash pond leachate is of great importance. Serial batch leaching was carried out simulating the rainwater condition of the study area to understand the behaviour of elements during leaching. The leachates were analysed for the elements Al, Ca, K, Mg, Na, P, S, Si, As, Ba, Fe, Mn, Mo, Ti, V, Pb, Zn, Co, Cr, Cu, Ni and Cd by inductively coupled plasma optical emission spectrometer (ICP-OES). It was found that Cd, Co, Cr and Ni did not leach from the ash while Cu and Pb concentrations were insignificant in the leachate regardless of liquid to solid (L/S) ratio. Most of the elements showed maximum concentrations at lower L/S ratio and then decreased with increasing L/S. The total cumulative concentrations of As, Mn and Mo were found to be higher than the World Health Organization (WHO) recommended values for drinking water while the concentrations of Fe, Mn and As exceeded the maximum allowable concentrations prescribed by the United States Environmental Protection Agency (USEPA). The pre and the post leached ash samples were analysed for morphology, specific surface area and mineralogical changes. Analysis of post-leached fly ash indicated changes in the specific surface area and morphology but no change in mineralogy.

Sorption and distribution of adsorbed metals in three soils of India

Abstract The mobility and bioavailability of heavy metals depends on the metal retention capacity of soil and also on the geochemical phases with which metals are associated. Laboratory batch experiments were carried out to study the sorption and distribution of Cd, Ni and Pb in 3 soils differing in their physicochemical properties from India: Oxyaquic Haplustalf (SL1), Typic Haplustalf (SL2) and Typic Haplustert (SL3). The heavy metal adsorption was studied by isotherms and the distribution coefficient ( K D ) for each metal was obtained from the linear regressions of the concentration of metal remaining in equilibrium solution and the amount adsorbed. In general, the sorption capacity for all the metals decreased in the order: SL3>SL2>SL1. Among metals, the sorption capacity in all the soils decreased in the order: Pb>>Ni>Cd. Distribution of sorbed metals at various equilibrating concentrations was studied by sequential extraction. Results showed significant differences in the distribution of metals in these soils. At higher additions (such as 200 μM l −1 ) most of the metals were extracted in their more mobile fractions, exchangeable and/or inorganic in contrast to their original partitioning in soils, where they were preferentially associated with the less mobile residual fraction. Largest percentages of metals extracted in the exchangeable fraction corresponded to those soil–metal systems with smaller K D values, e.g. Cd, Ni and Pb in SL1 and Cd and Ni in SL2. In neutral and alkaline soils (SL2, pH=7.1, and SL3, pH=8.6) Pb was predominantly extracted from the inorganic fractions and this corresponded to higher K D values for Pb in these soils. The predominance of metals associated with the exchangeable fraction together with low K D values indicates higher mobility of metals retained in the acidic soil (SL1, pH=5.2) compared with the others.

Delineation of groundwater contamination around an ash pond: Geochemical and GIS approach

The study has investigated the levels of metal contamination in groundwater due to particulate matter fallout and leaching from ash pond and assigned contamination indices for the adjacent localities around an ash disposal site with application of geographic information systems (GIS). Fe, Ba, Cu, Mn, S, Pb, V, and Zn were found to be the major contaminants in groundwater. Enrichment factors (EF) of these elements with respect to the United States Environmental Protection Agency (USEPA) maximum contaminant levels show high values for Mn, Fe, and Pb in groundwater. The zone of attenuation for Ba, Fe, Cu, Mn, S, and Zn in groundwater is about 600-900 m from the ash pond, while Pb did not show any significant attenuation even at a distance of 1200 m. Tube wells around Rankasingha and Kukurhanga villages are most contaminated whereas open wells of Lachhmanpur, Kaniapada, and Kurudul villages showed higher degrees of contamination.

Heavy Metals Adsorption and Their Distribution in Three Soil Types of India: Effect of Coal Fly Ash and Sewage Sludge Amendment

Even though both coal fly ash and sewage sludge are rich sources of bio-essential nutrients, one of the major limiting factors in their use either individually or in mixture proportions as for amendment into agricultural soil is the presence of various metals likely to be potentially toxic at their elevated concentrations. This study evaluated the adsorption and distribution behaviours of selected metals in three different soils from India amended with mixtures of ash and sludge in various proportions at a maximum application rate of 52t ha−1 and incubated up to 90 days at near field capacity moisture level. The properties of amended soils were affected significantly by sludge than the ash and the Freundlich distribution coefficients (KDs) of metals were marginally higher compared to their respective controls. The degree of impact of amendment on soil properties, distribution coefficients of metals and their adsorption affinity sequences, based on KDs, within and across soil types were determined. Sequential extraction indicated that, the concentrations of native metals in each soil type tends to be less in highly mobile and moderately mobile fractions than the resistant; and changed marginally following amendment while the distribution patterns remained more or less undisturbed. The sequential extraction of adsorbed metals at various equilibrating concentrations of their addition indicated shifts in the distribution patterns in each soil type. However, the changes in the partitioning of adsorbed metals were wide and clearly noticeable only at higher loadings and the metals showed propensity to accumulate preferentially in more mobile fractions, depending on the type of soil surface and substrate. The results indicated that at low rate of application, ash and sludge, though capable of changing the soil properties and its metal adsorption capacities to certain extent; they had no major influence on metal distribution patterns in the amended soils which mainly depended on the soil properties, type of metal and its concentration.

Heavy Metal Distribution and Bioavailability in Coal Ash and Sludge Amended Acid Lateritic Soil Under Field Conditions

Chemical fractionation of heavy metals in ash, sludge and amended soil was performed using sequential extraction. The metals were predominantly found to be present in the residual and carbonate fractions in the native soil and ash while amounts of Ni, Cd and Zn were significant in the exchangeable fractions of sludge. The distribution of metals in the extractable fractions differs according to the metal extracted, the treatment and the proportions of application. Among the metals, Ni and Zn and to a lesser extent Cd moved readily in the sludge amended soils due to lowering of pH and simultaneous increases in their most labile forms. Better yields of paddy and peanut with ash addition and reduction with sludge proportion were observed. The paddy straw and peanut shoot showed the maximum accumulation of metals indicating a physiological barrier in the transfer of metals from the shoot to the grain. Linear relationships were observed between the soil total metal concentrations with that in the crops. The study indicated that at the applied rate, the behavior of heavy metals in the amendments was primarily controlled by sludge.