The global community faces a dual environmental challenge: the pollution of water bodies from excess phosphorus and the rapid depletion of finite phosphate rock reserves. In a recent study published in Industrial Crops & Products, researchers Meiling Zhang, Yu Li, Shuang Ai, Xianghui Meng, Jianghao Cheng, Zhuqing Liu, Fan Yang, and Kui Cheng present an innovative, two-pronged solution to this problem. They developed a novel, engineered biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More modified with magnesium oxide (MgO-BC) to efficiently extract phosphorus from wastewater and then convert it into a slow-release fertilizer. This research highlights the significant potential of MgO-BC as a sustainable material that integrates waste management with agricultural enhancement within a circular economy framework.

The team synthesized a honeycomb-like MgO-BC using a chemical foaming strategy, with corn stalks as a base and magnesium bicarbonate as both an activation agent and metal source. This process resulted in a highly porous structure with an optimized surface area that is critical for superior adsorption. The engineered biochar demonstrated a maximum theoretical adsorption capacity of 189.90 mg/g, a value that surpasses many other adsorbents documented in the literature. The primary mechanism for this efficient phosphorus removal is chemisorption, predominantly governed by electrostatic interactions and complexation reactions. The optimal concentration of magnesium bicarbonate was found to be 0.5 mol/L, as higher concentrations led to the agglomeration of MgO, which obstructed pores and reduced adsorption efficiency.

Once saturated with phosphorus, the MgO-BC was tested for its ability to function as a slow-release fertilizer. In field and laboratory tests, the phosphorus-loaded biochar (MgO−BC−P_ads) successfully released 59.02% of the absorbed phosphorus into the soil over a 35-day period, demonstrating a controlled and consistent release rate. This contrasts sharply with traditional superphosphate fertilizer (CF), which showed a sharp initial surge in phosphorus release, peaking at 44.25 mg on day 21, followed by a more gradual release. The slow-release performance of the MgO-BC-Pads aligns with the Chinese national standard for slow-release fertilizers, ensuring that nutrients are delivered steadily and without the risk of rapid nutrient loss or environmental issues like eutrophication.

The positive impact of the MgO-BC on crop growth was quantitatively assessed through a pot experiment with bok choy. The MgO−BC−P_ads treatment significantly increased the bok choy’s dry weight by 131.58%, leaf length by 14.37%, and leaf number by 57.14% compared to the control group. The fertilizer’s slow-release properties compensated for a slight delay in germination and ensured a continuous supply of available phosphorus (AP) throughout the growth cycle, effectively meeting the crop’s nutritional demands. The study also revealed a remarkable improvement in root development, with root length increasing by 52.24% and root surface area by 76.39% compared to the superphosphate treatment. This enhanced root system is crucial for improving nutrient and water absorption efficiency.

Beyond crop productivity, the application of MgO-BC also improved soil health. It led to a notable increase in dissolved organic carbon (DOC) levels, attributed to the biochar’s carbon content and its unique hierarchical pore structure that facilitates carbon storage in the soil. Furthermore, concentrations of available potassium (AK) in the soil increased by over 30%. The study concludes that the chemical foaming technology used to produce MgO-BC successfully addresses the limitations of conventional modification methods by creating a highly efficient material without generating toxic byproducts, thus providing a green and sustainable pathway for large-scale production.

SOURCE: Zhang, M., Li, Y., Ai, S., Meng, X., Cheng, J., Liu, Z., Yang, F., & Cheng, K. (2025). Engineered biochar with MgO impregnation: A phosphorus vector bridging aquatic systems and agricultural soils via targeted adsorption and controlled release. Industrial Crops & Products, 234, 121596.