Table 3.

Physiochemical processes

Treatment method	Wastewater	Removal efficiency	Highlights	References
Physical method/adsorption	Steel industry	Fe2+: 99.7 Pb2+:99.9 Zn2+:98.9 Cr6+: 99.9	The treated clay exhibited consecutive reuse in four adsorption cycles while reducing the physicochemical variables to acceptable levels. Following the adsorption that, measurements indicated that the treated wastewater met the environmental requirements.	(Lawal Odebunmi and Adekola 2020)
Physical method/adsorption	Blast furnace	Cyanide: 99.5	The adsorption of cyanide on LDH exhibited a physisorption nature, with the dominating mechanism being ion exchange. The synthesized LDH material could be regenerated using a mixture of sodium hydroxide and sodium nitrate, allowing successful reuse for up to five cycles with an elimination rate of 85%. Additionally, the efficiency of LDH reuse could be enhanced by calcining it at 650°C.	(Ravuru et al. 2019)
Chemical method/electrocoagulation combined with photo-Fenton	Steel plant	COD:98 Phenol:100	The results clearly demonstrate the efficacy of the EC-PF process for eliminating organic substances such as phenol from water. The process exhibits superior elimination rate and proves to be more cost-effective when compared to alternative removal methods.	(Malakootian and Heidari 2018)
Chemical method/Photo-degradation and UV irradiation	Steel industry	Cyanide: 90	The presence of dissolved oxygen had a significant role in the degradation process. Initially, the rate of photo-decyanation was rapid, gradually decreasing over time. This observation ensures the process's industrial viability, as it indicates a sustainable and controlled degradation rate.	(Biswas et al. 2020)
Chemical method/ Ozonation	Coking	Cyanide: 94 COD: 72 BOD: 75	The integration of ozonation and EC proved highly efficient in lowering the levels of cyanide, COD and BOD. An initial cost analysis estimated a cost of 5.801 US$ per cubic meter (m3)	(Das, Anweshan, et al. 2021)
Physical method/filtration treated coking effluent	RO	COD: 85 ammonium nitrogen: 95 TOC: 85	The phytotoxicity was notably lower after treatment via a sand bed and reverse osmosis (RO). After just the sand bed, the wastewater still exhibited toxicity. Among the treatment methods, the reverse osmosis process resulted in the lowest toxicity levels observed in the wastewater.	(Smol et al. 2018)
Chemical method/chemical precipitation	Stainless steel	Cu:99.7 Mn: 99.7	The research demonstrated that the electric arc furnace dust slag by itself is capable of significantly removing the target metals, thereby lowering the expenses associated with acquiring expensive chemicals. The addition of a small quantity of Ca(OH)2 resulted in the elimination of both metals, achieving an impressive efficiency of 99.7%.	(Forsido et al. 2020)
Chemical method/precipitation	Plating	Cu: 93.9 Zn: 99.3 Cr3+: 99.9	Sulfide precipitation exhibits superior elimination capabilities for mixed heavy metals, resulting in lower levels of total suspended solids when compared to hydroxide precipitation.	(Yatim et al. 2021)