Razi University Journal of Applied Research in Water and Wastewater 2476-6283 12 2 2025 12 01 Mechanisms of solution pH effects on the adsorption process efficiency: A theoretical and experimental study 144 149 3890 10.22126/arww.2025.11358.1348 EN Mukhtar Dhajir Shubber Al-Qadissiyeah Environment Directorate, Ministry of Environment, Al-Qadisiyah, Iraq. 0009-0008-5660-1119 Mohammed Kadhum Al Kasser Department of Environmental Science, College of Science, University of Al-Qadisiyah, Al-Qadisiyah, Iraq. 0000-0001-8443-5439 Daryoush Yousefi Kebria Department of Environmental Engineering, Civil Engineering Faculty, Babol Noshirvani University of Technology, Babol, Iran. 0000-0001-7983-1568 Journal Article 2024 11 08 The study aims to show the role of pH value and the feasible mechanisms that affect the adsorption capacity by the theoretical concept and experimental work. The protonation, ionization, hydrophobicity, dissociation, precipitation, hydrolysis, hydroxylation, electrical repulsion or interaction, ion exchange, and complexation and chelating are effective mechanisms that have been studied theoretically to show their essential role in the absorption process and how they are affected by the pH value. Moreover, using varied pH values (2, 4, 6.5, 9, 11, and 13) to verify experimentally the role of the studied mechanisms on the adsorption capacity utilizing the recycled bentonite waste as adsorbent to adsorb the heavy metals, methylene blue dye, and engine oil as adsorbates from aqueous solution. It was apparent that the pH solution has an influential role in the adsorption capacity and from the difficulty in predicting the effect without making the experimental investigations due to the nature of the adsorbent and adsorbate that affected the ten mechanisms where the pH of the high adsorption capacity for heavy metal was alkaline (>11) and for the methylene blue and engine oil was neutral(≈ 6.5). https://arww.razi.ac.ir/article_3890_b823ab171ed0d81ba06bf175eea8e58c.pdf