Abstract
Coal fly ash obtained from a local power station was used as an adsorbent in the removal of sulphates in an aqueous solution. The coal fly ash was characterised using an x-ray fluorescence (XRF) which revealed that it was class C and sub-bituminous type fly ash, an x—ray diffractometer (XRD) which revealed the dominance of a large amorphous phase and a Fourier Transform Infrared Spectroscopy (FTIR) which showed the presence of both organic and inorganic functional groups. Adsorbent dosage, contact time, temperature and solution pH were varied and all the parameters showed a higher uptake of sulphate ions with their increase, except pH which showed a decreasing uptake. The pseudo second order model showed a better fit for the sorption data with lower error values than the pseudo first order model. The uptake of sulphate ions followed both the Langmuir and the Freundlich isotherm models with RL values for the Langmuir within the range 0 < RL < 1 and n-values for the Freundlich within the range 0 < n < 10 showing a favourable sorption for both models. All the thermodynamic parameters (ΔG°, ΔH° and ΔS°) were positive indicating a non – spontaneous, endothermic and a random solid – liquid interface. The process was shown to follow a unimolecular layer approach with chemical adsorption as the dominating mechanism. Generally, coal fly ash showed a higher affinity for sulphates leading to its effective removal.
Highlights
The purification of water is a wide – ranging process intended to obtain characteristics such as colourless, tasteless, odourless, non – corrosive and clear effluent with sufficient quality for human consumption
This study investigated the feasibility of using coal fly ash as an adsorbent for the treatment of sulphate rich process effluents
Fly ash was obtained from a local power station which was used as an adsorbent and analytical grade chemicals obtained from Sigma Aldrich through a local supplier were used to prepare the conditioning agent, synthetic waste water and standards for calibration of Ultraviolet-Visible Spectrophotometer (UV-Vis)
Summary
The purification of water is a wide – ranging process intended to obtain characteristics such as colourless, tasteless, odourless, non – corrosive and clear effluent with sufficient quality for human consumption. Industrial wastewaters with high sulphate concentration include acid mine drainages, textile effluents and tanneries. Remediation technologies that have been used to remove sulphate ions in wastewaters include active neutralisation by lime, limestone biological sulphate removal and alkaline barium calcium desalination process [6]. These liming agents produce a large volume of sludge which requires disposal and the process has proven to be very costly [7] but studies have been conducted in recent years to find alternative ways to remove sulphates in a more cheaper, efficient and environmentally friendly way. One of the wastewater treatment technologies that has gained attention is adsorption which has shown its capability to remove toxic waste from industrial effluents [2]
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