Abstract
In this study, we were aiming at testing halloysite nanotubes as an efficient adsorbent for the removal of phosphate from agricultural runoff. Adsorption of phosphate onto powder and granular form of halloysite nanotubes has been examined by using the classical batch method and diffusion experiments at room temperature. Different forms of halloysite nanotubes were investigated to explore the effect of structure on the adsorption of phosphate. The maximum adsorption efficiency was obtained for powder halloysite nanotubes (79.5%) and granular form (94.7%). It is believed that the pore space of the granular halloysite nanotubes accommodates phosphorus in addition to physico-chemically bound phosphate at surfaces. The pseudo-first order and pseudo-second order model fitted well the experimental kinetic data for both powder and granular form of halloysite nanotubes. The fit of the Freundlich isotherm model was superior as compared with the Langmuir approach, implying that the halloysite nanotubes are heterogeneous because of multiple surface groups and different pore structures. The two forms of halloysite nanotube tested have the abundant potential for removal of phosphate from agriculture runoff. Additional investigations at the pilot scale are, however, required to draw definite conclusions.
Highlights
Excessive phosphate discharge from manure, sludge sources, and chemical fertilizer applied to agricultural soils to runoff is the prominent source of water quality deterioration and nutrient enrichment
Surface characterization depicts that the specific surface area of Halloysite nanotubes (HNTs) ranges from 25 to 35 m2 g−1, which is principally appealing for phosphate adsorption
The nanotubes was studied via diffusion and batch experiments. Both powder and granular halloysite nanotubes was studied via diffusion and batch experiments
Summary
Excessive phosphate discharge from manure, sludge sources, and chemical fertilizer applied to agricultural soils to runoff is the prominent source of water quality deterioration and nutrient enrichment. Coagulation, ion exchange, biological, and physical treatments have been reported to remove phosphorus from aqueous solutions before it discharges to agricultural runoff [10,11,12]. Reverse osmosis, and adsorption seem to be highly promising as compared to chemical treatments to remove phosphate from aqueous solutions [14]. Several adsorbents have been investigated in various studies for the removal of phosphate from aqueous solution such as nanoparticles [19,20], nanoscale zero-valent materials [21], activated red mud [22], Water 2019, 11, 203; doi:10.3390/w11020203 www.mdpi.com/journal/water
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