Fly Ash Use as an Amendment and Fluoride Adsorbent in Sodic Soil

Abstract

Sodic soilsare best reclaimed so far by using chemical amendment like Gypsum (CaSO4.2H2O)which is a rich source of Calcium. This chemical provides sufficient Ca2+ions that replace the exchangeable Na from soil exchange complex and reducesthe sodicity. A large-scale use of such chemical amendments has been restricteddue to its diminishing stock and economic considerations. Therefore, theefforts are being made to find more viable and cost effective method forreclamation of vast patches (3.77 million ha) of sodic soil in India. Thisnecessitates a need to explore the possibilities of utilizing fly ash as anamendment for the reclamation of sodic soils. As per the estimates, fly ashgeneration is expected to increase to about 225 million Mg by 2017. This largevolume of fly ash occupies large area of land and possesses threat toenvironment. Therefore, there is an urgent and imperative need to adapttechnologies for utilization and safe management of fly ash on sustainablebasis. Agriculture sector could be emerged as a prime user for fly ash in thecountry.  The main components of fly ashare SiO2 (52.7%); Al2O3 (21.9%), Fe2O3(8.4%), and CaO (7.2%), MgO (1.25%) and residual carbon. However, thepercentage varies from source of the coal used in the thermal power stations.The pH range of fly ash has been reported from 4.5 to 12.0. Its particle sizemay have a significant role in improving soil physical and chemicalcharacteristics of soil. It provides micro nutrients (Fe, Zn, Cu, Mo, B, Mn)and macro nutrients (K, P, Ca, Mg, S). The problem of high fluorideconcentration in groundwater resources has become an important health-relatedgeo-environmental issue worldwide. India is confronting the sameproblem and at present at least 20 states have become endemic tofluorosis.  The use of fly ash asamendment will not only ameliorate the sodic soils but also acts as a goodadsorbent for fluoride. The fineness of the fly ash particles and the inherentlarge surface area (1 to 6 m2 g-1) together with thecontent of un-burnt carbon, make it a good agent for utilization as aninexpensive sorbent. Hence, in conclusion the fly ash may not only be afeasible alternative to gypsum for amelioration of sodic soils but also used asa good adsorbent of fluoride in sodic soils, thereby reducing the fluoridecontamination in the groundwater from soil.