# Evaluation of Agricultural Soil-Improving Zeolite for Improving Irrigation Water Quality
## 4 Conclusions  
This study addressed the issue of water quality in an irrigation reservoir with high levels of boron (B) and sodium (Na)--9.7 and 0.75 meq/L, respectively--which adversely affect the development of sensitive crops such as citrus. It is crucial to highlight that this study, utilizing zeolite as a sorbent, was conducted in a context where this material was already employed as an agricultural soil amendment in southeastern Spain, an area where irrigation water quality is often compromised. The results indicated that sodium removal exhibited limited efficiency (10-24%), with desorption observed in some cases, underscoring the challenges of combined removal \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Boron** & **Sodium** \\ \hline \multicolumn{3}{c}{**Pseudo-first-order**} \\ \hline R\({}^{2}\) & 0.9660 & 0.9406 \\ \hline K\({}_{1}\) (L min\({}^{-1}\)) & 0.01 & \(-\)0.20 \\ \hline q\({}_{\rm e}\) cal (mg g\({}^{-1}\)) & 0.42 & 0.88 \\ \hline \multicolumn{3}{c}{**Pseudo-second-order**} \\ \hline R\({}^{2}\) & 0.9349 & 0.5913 \\ \hline K\({}_{2}\) (g mg\({}^{-1}\) min\({}^{-1}\)) & \(-\)0.65 & \(-\)0.03 \\ \hline q\({}_{\rm e}\) cal (mg g\({}^{-1}\)) & 0.02 & \(-\)0.34 \\ \hline h (mg g\({}^{-1}\) min\({}^{-1}\)) & \(-\)1.86 \(\times\) 10\({}^{-4}\) & \(-\)3.78 \(\times\) 10\({}^{-3}\) \\ \hline \multicolumn{3}{c}{**Intraparticle diffusion**} \\ \hline R\({}^{2}\) & 0.7902 & 0.3337 \\ \hline K\({}_{\rm in}\) (g mg\({}^{-1}\) min\({}^{-1/2}\)) & 2.89 \(\times\) 10\({}^{-6}\) & 0.028 \\ \hline \end{tabular} where q\({}_{\rm e}\) represents the amount of sorbate retained (mg) per gram of sorbent at equilibrium; K\({}_{1}\) and K\({}_{2}\) are the rate constant of the pseudo-first-order and pseudo-second-order, respectively; and K\({}_{\rm in}\) is the rate of intraparticle diffusion.  
\end{table} 
Table 8: Kinetic parameters for B and Na removal onto zeolite. with boron and various elements present in natural irrigation waters. On the other hand, boron removal demonstrated higher efficiency (up to 100%) under specific conditions, with significant interactions and influences from other chemical species present in water and zeolite composition. Statistical analysis, including analysis of variance (ANOVA), identified significant factors for boron removal (zeolite content and contact time) but not for sodium. Based on statistical significance and practicality, optimal conditions for boron removal were determined as 4.93 g of zeolite/L and 723 min of contact time. Kinetic studies revealed differential behaviors for sodium and boron, with cyclic sorption/desorption observed for sodium and slow, steady sorption for boron. The pseudo-first-order model was found to be applicable for both cations, indicating a physical or physisorption process, while the pseudo-second-order model suggested possible chemisorption for boron. pH variations during the process indicated a slight decrease, potentially explaining lower sodium adsorption, aligning with literature suggesting higher sodium adsorption at a higher pH. The study paves the way for future research, particularly in understanding the complex interactions influencing the sorption behavior of sodium and boron on zeolite under dynamic conditions. The findings contribute to the optimization of zeolite-based treatments for agricultural irrigation water, providing insights into challenges and potential solutions for sodium and boron removal. Conceptualization, D.N.-G. and P.M.; data curation, D.N.-G.; formal analysis, D.N.-G.; funding acquisition, P.M.; investigation, D.N.-G. and P.M.; methodology, D.N.-G.; project administration, P.M.; software, D.N.-G.; supervision, J.J.M.-N. and P.M.; validation, P.L., A.C. and J.J.M.-N.; visualization, P.L. ; writing--original draft, D.N.-G.; writing--review and editing, D.N.-G., J.J.M.-N. and P.M. All authors have read and agreed to the published version of the manuscript.