Recuperação de fósforo de efluente líquido de parboilização de arroz e avaliação como potencial fertilizante de liberação lenta a partir de nanocompósito à base de nanomateriais lamelares e biopolímeros

Abstract

The rampant rate of population growth in recent decades has demanded an exacerbated use of fertilizers in the agricultural sector to meet global food demand, leading to the depletion of natural resources and negative environmental impacts such as eutrophication. In this context, the objective of this research was to synthesize a nanocomposite of alginate hydrogel (ALG) and polyvinyl alcohol (PVA) incorporated with layered double hydroxides (LDH) based on steel slag, evaluating its efficiency in the recovery of phosphorus from washing effluent of parboiled rice, and potential use as a slow-release fertilizer. LDH synthesis was performed by the coprecipitation method in variable pH up to a value of 12, resulting in two groups of samples of LDH12-25 (pH=12, T= 25°C) and LDH-12-65 (pH= 12, T=65°C). The LDH was characterized by the FRX, EDX, SEM, DRX, and BET techniques. A higher concentration of calcium and iron cations was found in these, with the majority crystalline phase being iron and calcium hydroxysilicate-like compound (Ca3Fe2Si1,15O4,6(OH)7.4) (35.2%). Subsequently, the nanocomposites were formed with 8% (m/v) of LDH in ALG-PVA (concentration of 1% [m/v] and 0.5% [m/v]) and submitted to an adsorption batch test. (24h, 25ºC, and 125 rpm, adsorbent dosage from 3 gL-1 to 11 gL-1 ). It was found that the LDH-12-25 sample presented both textural (surface area of 87.084±4.919 m²/g) and morphological characteristics (regular crystals with dimensions of 168 ± 45 nm) more favourable, the better performance in phosphorus recovery (91.33±0.70%) of diluted effluent (factor 1:10, C0= 10 mg.L-1 ) when incorporated in ALG-PVA. The isotherm profile was considered favourable, with the Langmuir and Freundlich models being consistent with the results (R²> 0.9). The maximum adsorption capacity calculated assumed an average value of 1.583 mg. g1, following worldwide research cited in this work. Finally, when the sample ALG-PVALDH-12-25 was submitted to a kinetic test of phosphorus release, a release of 95.36% was verified over 14 days of testing, suggesting a linear release curve. Therefore, it was evidenced a promising technology of phosphorus recovery with controlled release, becoming an alternative to supply the global demand for fertilizers as well as decreasing natural resources depletion such as phosphate rocks.