Phosphate and nitrate sorption by amine-modified silica as the study of slow release fertilizer

Abstract

The mud of Lapindo was reported consisted of significant amount of silica that have great capability to adsorb cations and anions due to their large surface areas. The properties of silica can be investigated in the purpose of binding cations and/or anions of micronutrients and releasing them when they are dissolved into water. The measurement of the release rate would give good description of the principle of slow release fertilizer. This research studied preparation of silica from Lapindo mud, that be treated become silica gel (SG) or whose surface were modified by use of (3-Aminopropyl)triethoxysilane (APTES) become amine-modified Silica (AMS). The sorbent was used for adsorption experiments of phosphate (H₂PO₄ ⁻) and nitrate (NO₃ ⁻) ions. Both ions bound the sorbent of AMS through hydrogen bonding. Phosphate formed monolayer surface complexes, but nitrate formed multilayers surface complexes with the sorbent. Desorption results showed that AMS bound phosphate ions stronger than SG. Rate constant of desorption (k) of phosphate by SG and AMS were 0.00507 and 0.000107 g.mmol⁻¹.mint⁻¹ respectively. However, the nitrate desorption by SG were smaller than that by AMS as indicated by k of 0.000268 and 0.000836 g.mmol⁻¹.min⁻¹ respectively