Optimization of the production of a complete fertilizer formulation by batch impregnation using clinoptilolite zeolite as carrier

Abstract

Fertilizer inefficiencies caused by uncontrolled and rapid nutrient release pose serious environmental threats and economic losses. Adsorption of nutrients in carriers such as clinoptilolite zeolite (CZ) has been proven to be effective in minimizing environmental pollution and improving the duration of nutrient availability in soil. In this study, a complete fertilizer was formulated via the batch impregnation of the combination of nutrient sources, such as urea, calcium hydroxyapatite (CaHAp), and muriate of potash (MoP), in CZ carrier in a 1:1 ratio. Carrier pre-treatment was done by washing CZ with deionized water and ethanol, followed by calcination at 600 °C for 4 hours. The process has 86.92% recovery and increased the cation exchange capacity (CEC) of the carrier from 41.30 cmol(+)/kg soil to 47.7630 cmol(+)/kg soil. The effect of mixture factors (% Urea : % CaHAp : % MoP ratio) and process factors (mixing time and sonication time) on the total nitrogen (N), phosphorus (P), and potassium (K) content was investigated using an Optimal (Combined Mixture) Experimental Design. Statistical analysis showed the direct effect of the mixture factors and the insignificant effect of the process factors on the said responses. The optimum conditions obtained via numerical optimization is as follows: (1) 50 : 23.99 : 14.61 : 11.39 (% PCZ : % Urea : % CaHAp : % MoP) ratio, (2) mixing time of 158.57 minutes, and (3) sonication time of 30 minutes. This resulted to a fertilizer with a total N, P, and K content of 4.65 % 2.76 %, and 5.42 %, respectively. Moreover, it has about 1.96 % bound N, 0.28 % bound P, and 2.93 % bound K due to a successful adsorption process. The adsorption process has a high fertilizer yield of 96.49 %. DLS analysis revealed that the optimized product has an average particle size of 4105.8 nm; thus, it cannot be characterized as a nanofertilizer. Cost analysis showed that the formulated complete fertilizer is priced at Php 465.82 per kilogram, which is more expensive than the 14-14-14 conventional fertilizer due to higher cost of production. However, the possible slow/controlled release property of the NPK-PCZ fertilizer could offset the high price due to longer availability of nutrients in soil. As such, this could mean lower rate of fertilizer application thus allowing to save up in resources and manpower.