Analysis of the simultaneous adsorption mechanism of ammonium and phosphate on magnesium-modified biochar and the slow release effect of fertiliser

Abstract

To decrease the eutrophication caused by nitrogen (N) and phosphorus (P) in water, magnesium-modified corn stalk biochar (MgB) was prepared under the synergistic impact of the multi-pyrolysis temperatures and Mg2+ contents for the co-adsorption of ammonium (NH4+-N) and phosphate (PO43−). The co-adsorption mechanism, slow-release performance and plant application of MgB were systematically studied. The results showed that pyrolysis temperatures (350–650 °C) and Mg2+(0–3.6 g/L) contents not only altered the physicochemical properties of biochar, but also significantly affected the adsorption efficacy of MgB. The adsorption of NH4+-N and PO43− was in accordance with Langmuir–Freundlich and pseudo-second-order kinetic models (Qmax = 37.72 and 73.29 mg/g, respectively). Based on the characteristics, adsorption kinetics and isotherms results, the adsorption mechanism was determined and found to mainly involve struvite precipitation, ion exchange, and surface precipitation or electrostatic attraction. Compared with the leaching performance of chemical fertilizers (CF), after adsorption of NH4+-N and PO43− (MgB-A), MgB had a more stable pH and lower conductivity. Leaching of NH4+-N and PO43− by MgB-A was controlled by both the diffusion mechanism and the dissolution rate of struvite and Mg-P. The excellent long-term slow-release performance and abundant Mg2+ of MgB-A promoted the growth of Zea mays L. and Lolium perenne L. Overall, this study suggested that MgB could realize a win–win outcome of struvite biochar-based fertiliser production and wastewater treatment.

Adsorption and Removal of Phosphate from Wastewater Using Lignin-Based Adsorbent Modified with Lanthanide: Characterization, Performance, and Mechanisms

“…The core of the adsorption process is the adsorbent, which impacts adsorption performance in four aspects: adsorption capacity, adsorption selectivity, adsorption/desorption rate, and regeneration . Many adsorbents have been reported, such as mesoporous materials, carbon nanotubes, biochar, − hydrogels, CeO 2 particles, and graphene . These adsorbents were used on a laboratory scale; however, there still exist some problems during the industrial application that need to be resolved immediately, such as the high cost, complex synthetic route, and difficulty in recycling.…”

Nitrate Absorption and Desorption by Biochar

“…The nutrient release performance from biochar was related to ion binding capacity and absorption level [16]. Therefore, in addition to optimizing the biochar application rate, biochar modification for absorption capacity and strength has become an inevitable trend to enhance its slow-release effect [107]. Commonly used methods include chemical and physical modifications, with chemical modification being the most extensively employed method.…”

Synthesis of biochar‐embedded slow‐release nitrogen fertilizers: Mesocosm and field scale evaluation for nitrogen use efficiency, growth and rice yield

“…Compared with conventional urea and NH 4 Cl, N from biochar‐embedded fertilizers was released at a significantly slower rate ( p < .05) during the incubation period, allowing more N to be retained in the fertilized soil to sustain plant N consumption for longer, as supported by Kim et al (2014) and Sun et al (2017) who reported that a biochar‐urea composite compared with chemical urea delayed N release and a wide ammonium‐nitrate ratio can be maintained over a longer period of time. We observed that N fertilizers may allow water to seep into biochar pores, causing osmotic pressure to build up, allowing BSRNF granules to break apart and further release urea and NH 4 Cl as any urea or NH 4 Cl found on the exposed surfaces of SRF pellets will be rapidly dissolved when exposed to water after being released into the soil (He et al, 2022).…”