Other than that, the carboxymethyl predominantly exist in the form of CH2COOH at low pH, and this prevent the metal ions being absorbed onto the hydrogel (Xu, Feng,Peng, Wang, & Yushan, 2005). Meanwhile, higher concentration of hydrogen ions from the hydrochloric acid that have been used to adjust the pH also effectively leads to reducing of ligands for metal ions binding during sorption (Gurgel & Gil, 2009).