Elemental composition and release characteristics of some South African fly ashes and their potential for land application

Eight fly ash samples collected from South African power stations were evaluated for various chemical properties, liming potential and metal species release under incubation. All fly ashes had alkaline pH ranging from 10.97 to 12.75 with much wider variations of electrical conductivity (range 0.46–8.27 dS m^?1). Their total P content ranged from 553.3 to 1514 mg P kg^?1 and Olsen extractable P from 130 to 345.5 mg P kg^?1. Application of two of the fly ashes to three different soils showed a high ability to neutralize acidity, resulting in an average of 41% change in pH after 8 weeks of incubation. Across all three soils, the fly ash incorporation increased extractable P content from a P-deficient level to levels above 25 mg P kg^?1 in two of the three soils. Except for Cu, all metal species (Cr, Pb, Ni and Fe) showed significantly (P ≤ 0.05) low extractability under fly ash treated soils compared to the soil alone control. These results suggest that the South African fly ashes studied are effective liming materials and can provide essential elements such as P with minimum risk of soil contamination from metal species release.