Application of hydrogeochemical modelling in simulating the transportation of elements in fly ash heap under different disposal systems in South Africa

Publication date: Available online 4 February 2015 Source:Physics and Chemistry of the Earth, Parts A/B/C Author(s): J.M. Mbugua , J.C. Ngila , A. Kindness , M. Demlie Ash heap modelling of South African fly ash from Tutuka was carried out and the duration of transportation projected for 20years based on two disposal scenarios, namely; irrigation of ash with rainwater, and irrigation with brines. The hydrogeochemical modeling code, PHREEQC, was applied in the study which gave insights into the speciation, release and transport of elements from the water and brines–fly ash long term interactions. Tutuka ash–water heap model showed a general sharp decrease of total elemental concentrations released during the first 2.5years simulation as the pH value dropped from 12.6 to 8.7, after which it remained constant and their concentration remained constant up to 20years. The elements showing this trend included Ca, Mg, Al, Fe, Sr, Zn, Na, K, Li and C(4). Generally, brines caused sharp increase in released concentration of the elements Ca, Mg, S(6) and C(4) for the first 3years of heap irrigation whereas with water irrigation an opposite trend was observed in which the elemental concentrations decreased. Much of the release chemistry of the elements was closely related to the phase dissolution/precipitation and formation as the major controlling factors. Generally therefore, the modelled leachate quality results revealed that many elements are mobile and move through the as...
Source: Physics and Chemistry of the Earth, Parts ABC - Category: Science Source Type: research