Carbon and Nutrient Sequestration Potential of Coal-Based Fly Ash Zeolites

Abstract

Disposal, safe management, and gainful utilization of coal-based fly ash are the issues of major concern and challenge in the present century due to alarming increase in the production of ash in India Recent reports indicated that fly ash utilization in agriculture sector has stood at 1.92 mt (million tones) during 2016–17, which constitutes hardly 1.14% alone of the total fly ash utilization. This might be attributed to low product value and presence of heavy metals in fly ash which limits its large-scale applications as agricultural soil amendments. Conversion of fly ash into zeolites (FAZ), a sodium aluminosilicates group of minerals, is an innovative and proven approach but not adequately researched under laboratory conditions to engineer the right quality of zeolite and field conditions to find out the slow nutrient release characteristics and the use efficiency under diverse soil types and agroecological conditions. The improved percent zeolitization of the FAZ will have twin benefits (water and nutrient retention) because of its fine loamy texture and high cation-exchange capacity (CEC). In addition, zeolites can conserve soil organic matter that will help further to improve the efficiency of soil water and nutrient use. This added property will be highly beneficial for tuber crops in particular as they are extensively grown in the country in degraded and marginally fertile soils poor in soil organic carbon (SOC) and as the economic parts are beneath the soil, the physical properties and SOC content are critical for the crop performance. With the funding support of fly ash unit, DST, during 2010–13, low-cost, high-value agricultural grade fly ash zeolites (near-neutral pH, low Na, high CEC, and low heavy metals content) was successfully synthesized and evaluated in sweet potato (Ipomea batatus L.) wherein the tuber yield was found correlated in soils amended with zeolites due to higher nutrient use efficiency with respect to the major nutrients studied, viz. N, P, and K. Research on large-scale field application especially on soil aggregation and compaction properties, soil carbon quality and stability potential aspects of FAZ, adsorption and availability of important soil nutrients NH₄⁺, K⁺, Ca⁺⁺, and Na⁺ must be given utmost priority to further establish the controlled release fertilizer characteristics of FAZ in India.