Jet loop reactor application for mine water treatment using fly ash, lime and aluminium hydroxide

Abstract

Recent studies have shown that a combination of coal fly ash (FA) and Al(OH) 3 can be used to treat neutral mine drainage (NMD) and reduce sulphate concentration to within South African drinking water quality levels, Class II (400-600 mg/L). The shortcomings of this method were the large amounts of FA required to raise the pH to greater than 11 (3:1 liquidto-solid ratio) so that Al(OH) 3 can be added to facilitate removal of sulphate ions through ettringite precipitation. This requires large silos to store FA, making upscaling of this treatment technology using normal mixing methods to be unrealistic. In the current study, a jet loop reactor was used to reduce the amount of FA needed to increase the pH to greater than 11. The pH was raised to greater than 11 by mixing 0.25 % of lime (w/v ratio) and 13 kg of coal FA with 80 L of NMD in a jet loop reactor. After the pH of the mixture was above 11, amorphous Al(OH) 3 (83.2 g) was added to the mixture. This resulted in the sulphate concentration decreasing to less than 500 mg/L. Bench-scale studies using 0.25 % (w/v) of lime and 6:1 coal mine water to FA ratio could not reduce the sulphate concentration to below 500 mg/L. Therefore, the impingement and cavitation mixing techniques that happen in a jet loop reactor played an important role in enhancing sulphate removal.

Treatment of acid mine drainage with coal fly ash in a jet loop reactor pilot plant

“…It is also a huge problem in the Mpumalanga coalfields. The few freshwater resources in Mpumalanga including the Vaal and Olifants rivers are threatened by AMD containing a high concentration of sulfate ions, Al, Fe, and Mn (Madzivire et al, 2015). The protection of water resources has become a fundamental policy concern as well as a driver for continued economic growth and service delivery to South Africa (Oberholster et al, 2010).…”

“…The jet loop reactor promotes a faster reaction rate by exerting a higher mass transfer rate and mixing intensity compared to a continuous stirred tank reactor. A high mixing rate in a jet loop reactor occurs due to hydrodynamic cavitation and impingement processes that occur inside the reactor (Vadapalli et al, 2008;Madzivire et al, 2015). Hydrodynamic cavitation is created by pressure variations due to the changes in the geometry of the system through which the solution is flowing.…”

Upscaling of Zeolite Synthesis from Coal Fly Ash Waste: Current Status and Future Outlook

“…The hydrodynamic cavitation is applied on a pilot plant scale within a jet loop reactor. In a study involving the scaling-up of a process to reduce sulphate concentrations within neutral mine drainage, a jet-loop reactor was used [69]. The study showed that the impingement and cavitation mixing techniques applied within the jet-loop reactor played an important role in enhancing the sulphate removal.…”

Mine Drainage Generation and Control Options

“…African drinking water quality levels (Madzivire et al, 2015). The pH was raised to greater than 11 by mixing lime (w/v ratio) with fly ash, and then amorphous Al(OH)3 was added to reduce sulfate concentration to less than 500 mg/L.…”