Asgari et al. (2013) found that the optimum pH foradsorption of phenol using zeolite was at 3. Ponizovsky and
Tsadilasc (2003) also noted that the use of clinoptilolite under
acidic conditions was efficient in phenol removal in accordance
with recommended values in the United States Environmental
Protection Agency regulations (USEPA, 2002). The acidity of TOMW
is favorable for arid KSA soils owing to compensation by the pre-
dominance of carbonate (CO2 À3 ) and alkalinity in this soil type
(Sierra et al., 2001).