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Directive, acid and reactive dyes are the carcinogenic dyes which have complex structures and difficult to remove from the industrial wastewater. In this study, coal fly ash (CFA) was modified with HCl and NaOH solution and used for the removal of direct fast scarlet 4BS, direct sky blue 5B, acid navy blue R, and reactive turquoise blue KN-G dyes. Laboratory experiments were carried out to analyze the performance of modified coal fly ash (MCFA) to check the removal efficiency and adsorption capacity of dyes. The maximum removal efficiency of direct fast scarlet 4BS and direct sky blue 5B were recorded 96.03% and 93.820%, respectively using 0.05 g adsorbent dosage at 100 mg/L initial concentration. The results of MCFA were compared with carbon black, chitosan, starch, zeolite and unmodified coal fly ash (UMCFA) at lower dosage 0.05 g and higher dosage 0.4 g. Adsorption isotherm were analyzed by Langmuir and Freundlich model by different dyes concentrations, the result stated that Freundlich and Langmuir model (±0.9918, ±0.9974) was fitted by chemisorption and physisorption methods for all four dyes. Adsorption kinetic were also determined by Pseudo-first-order and Pseudo-second-order at different contact times with dye molecules and adsorbent active sites, and the results showed that the adsorption behaviors of all four dyes were described better by pseudo-second-order kinetics than pseudo-first-order kinetics. Recommended dosage of modified fly ash is between 10 ‱ to 20 ‱ for simulated textile industrial waste water and regeneration temperature is 300 ℃. [Display omitted] • Coal fly ash was modified by HCl and NaOH for the dye adsorption. • After modification the surface area and porosity of CFA were increased. • Modified coal fly ash was used for the removal of directive, acid and reactive dyes. • Maximum removal efficiency of directive dye was recorded up to 98% by using modified CFA. • The results of MCFA were compared with carbon black, chitosan, starch, zeolite and unmodified coal fly ash. [ABSTRACT FROM AUTHOR]

• Physico-chemical properties of CFA were summarised in detail. • Leachability of CFA was analysed using six aspects. • Adverse effects of CFA on humans, wild animals, and plants were reviewed. • Utilisation of CFA in the USA and EU were summarised. • Directions for the reuse of CFA in the near future were proposed. Coal fly ash (CFA) is a valuable industrial solid waste, but conventional methods used for its disposal can lead to serious and long-lasting environmental issues. The study of technologies for CFA recycling has been of major concern, while the harm caused by CFA is only partially understood, limiting its reuse. In this review, the basic physico-chemical properties of CFA are introduced, followed by a systematic summary and discussion of the leachability of CFA via different leaching methods and the chemical speciation of some typical metal elements in CFA, which is related to its harmful effects. The specific harm that CFA causes to humans, wild animals, and plants and the study status of magnetic property of CFA are presented. Because of the pervasive concerns of many people, the utilisation of CFA in the USA and Europe and an economic and environmental analysis of its disposal is provided and discussed. Finally, some possible directions for future research involving CFA are proposed. [ABSTRACT FROM AUTHOR]