## 2 Experimental Design
### Heavy Metallic Ion Solution  
Due to a greater presence in various Ontario mine waste streams as presented by [PERSON] [40] and the strict limitations required by the Canadian Government [41], this study focuses on the presence of the heavy metallic ions of Pb\({}^{2+}\), Cu\({}^{2+}\), Fe\({}^{3+}\), Ni\({}^{2+}\) and Zn\({}^{2+}\)[32; 42]. The cations present in the sorbent have valences that differ from those in solution. Consequently, as the dilution increases, the selectivity of the adsorbent for the ion with a higher valence also increases. Accordingly, comparative analysis of various metal ions should be conducted at the same normality and temperature, in order to minimize the changes observed in isotherm configuration with dilution [43]. The synthetic metallic ion solutions are prepared from analytical grade nitrate salts in deionized distilled water, namely Pb(NO\({}_{3}\))\({}_{2}\) (CAS No. 10099-74-8), Cu(NO\({}_{3}\))\({}_{2}\cdot\)3H\({}_{2}\)O (CAS No. 10031-43-3), Fe(NO\({}_{3}\))\({}_{3}\cdot\)9H\({}_{2}\)O (CAS No. 7782-61-8), Ni(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O (CAS No. 13478-00-7), and Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O (CAS No. 10196-18-6), respectively, and combined equally to maintain a total normality of 0.01 N (10 meq/L). The five metals in a multi-component system of 2.0 meq/L per metal correspond to concentrations of approximately 207 mg/L for Pb\({}^{2+}\), 64 mg/L for Cu\({}^{2+}\), 37 mg/L for Fe\({}^{3+}\), 59 mg/L for Ni\({}^{2+}\), and 65 mg/L for Zn\({}^{2+}\), respectively. The NO\({}_{3}\)- anions in the aqueous solution do not influence the ion-exchange process, since they do not form any metal-anion complexes and do not hydrolyze in solution [13; 44].  
The uptake of multiple HMIs from aqueous solutions on natural zeolite is a complex process consisting of predominately ion-exchange and adsorption. At high initial concentrations, this process could be accompanied by precipitation and the metal ion hydroxo-complexes formed can be sorbed on zeolite surface sites that encompass different sorption affinity [13]. Research has demonstrated [26; 43; 45] that the sorbate solution acidity level affects the uptake of metals, and this is particularly the case for the HMIs that have low preference by zeolite. Such factors include the metal ion speciation and natural stability, as well as the electro-kinetic properties of zeolite in aqueous solutions. At a low pH level, the hydrogen cation (H\({}^{+}\)) is considered as a competitive ion to the HMI during the ion-exchange process [43]; evidently, the process is preferred at higher pH levels, which should be lower than the minimum pH of precipitation [10]. The pH level of the effluent solution decreases, depending on the metal removed. Therefore, the pH range under which sorption takes place should be specified [11].  
The Canada-Wide Survey of Acid Mine Drainage [40] reports a seasonal average of a majority of the mines surveyed to have documented pH values ranging from 2 to 5. This present study is conducted in the conservative end of this range, with the influent stock acidified to a pH level of around 2 with concentrated nitric (HNO\({}_{3}\)) acid (CAS No. 7697-37-2) [46], to prevent precipitation of  
\begin{table}
\begin{tabular}{c|c c c} \hline \hline \multirow{4}{*}{**Chemical Composition**} & Mineral Component & 85\%–95\%\  
the metal ions [14; 43]. With this low pH, however, the H\({}^{+}\) ion competition is significant, and so the removals obtained are on the conservative side and are lower than would normally be expected in field installations.