Effects of sodium alginate-poly(acrylic acid) cross-linked hydrogel beads on soil conditioner in the absence and presence of phosphate and carbonate ions

Abstract

Hydrogel beads, composed of polymers, possess the ability to absorb substantial quantities of water simultaneously and gradually release it in dry conditions. In this work, hydrogel beads were synthesized using sodium alginate (S-Alg) and poly (acrylic acid) (P-Acc), either in the absence or presence of phosphate (PO43−) (S-Alg/P-Acc@PO43−) and carbonate (CO32−) anionic ions (S-Alg/P-Acc@CO32−). Subsequently, these beads were crosslinked with Ca2+ ions. The scanning electron microscopy (SEM) images demonstrated that the presence of anionic ions has an impact on the structure of the hydrogel beads and enhances porosity expansion while concurrently reducing the concentration of carboxyl (COOH) groups. The hydrogel beads exhibited a great swelling behavior, with S-Alg/P-Acc@CO32− capable of absorbing up to 73.5 % of water in acidic conditions, but decreased under neutral and basic conditions. Soil water loss (SWL) experiments confirmed the ability of hydrogel beads to retain water in the soil. Additionally, observations of soil characteristics after a 14-day treatment revealed no significant difference in pH and C/N ratio (P-value <0.05). However, soil’s available Fe and N–NO3- significantly reduced (P-value <0.05) while substantially promoting soil N–NH4+, available phosphorus (P), cation exchange capacity (CEC), soil organic carbon (SOC), and exchangeable cation (Ca2+, K+ and Mg2+). The presence of hydroxyl (-OH) and –COOH groups was found to be crucial for enhancing soil properties.

Keywords

• Hydrogel beads
• Sodium alginate
• Poly (acrylic acid)
• Soil water retention
• Swelling
• Soil characteristics