Manawi, Y., Al-Gaashani, R., Simson, S. et al.Adsorptive removal of phosphate from water with 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 from acacia tree modified with iron and magnesium oxides. Sci Rep14, 17414 (2024). https://doi.org/10.1038/s41598-024-66965-3

Phosphorus, found primarily as phosphate in nature, is essential for the growth of plants and living organisms. However, the increasing demand for phosphate, mainly used in fertilizers, is causing significant environmental challenges, such as eutrophication in water bodies due to agricultural runoff. Effective removal and recycling of phosphate from wastewater is therefore crucial for both environmental and economic reasons. Recent research has explored a novel method using biochar derived from Acacia tortilis tree prunings, modified with iron (Fe₃O₄) and magnesium (MgO) oxides, to adsorb and remove phosphate from water.

Biochar, a carbon-rich material produced by pyrolyzing organic waste, has been widely recognized for its adsorptive properties. In this study, biochar was produced by calcining Acacia tortilis prunings at 600°C and then doped with iron and magnesium oxides through a hydrothermal process. This modification aimed to enhance the biochar’s surface area and charge properties, which are critical for efficient phosphate adsorption.

Unmodified biochar showed limited effectiveness in removing phosphate. However, the modified biochar demonstrated a significant improvement, removing nearly all phosphate from synthetic aqueous solutions with concentrations ranging from 1 to 500 ppm. The increased adsorption efficiency of the modified biochar is attributed to the enhanced surface charge and increased surface area resulting from the doping process. The specific surface area of the biochar increased by more than 20%, from 322 to 394 m²/g, after modification. Additionally, the point of zero electric charge (PZC) shifted from pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More 3.4 to pH 5.3, indicating a higher affinity for negatively charged phosphate ions.

The adsorption process was notably rapid, achieving 82.5% phosphate removal within the first 30 minutes and 97.5% after 4 hours. The maximum adsorption capacity was observed at 98.5 mg/g at a phosphate concentration of 500 ppm and pH 8.5. The adsorption data conformed well to the Langmuir isotherm model, suggesting a monolayer adsorption process on a homogenous surface.

Compared to other adsorbents reported in the literature, the iron and magnesium-modified biochar outperformed in terms of surface area, adsorption capacity, and removal rate. For instance, previous studies on biochars derived from peanut shells or Broussonetia papyrifera leaves exhibited lower surface areas and adsorption capacities, emphasizing the advantage of using Acacia tortilis prunings and the specific doping agents employed in this study.

The study further investigated the impact of different factors on phosphate adsorption. Increasing the biochar loading improved removal efficiency, but beyond an optimal point, the adsorption capacity plateaued due to saturation of adsorption sites. Higher solution temperatures also enhanced adsorption capacity, consistent with the endothermic nature of the adsorption process. The presence of co-existing ions, such as chloride and sulfate, slightly reduced phosphate adsorption but did not significantly impair the overall effectiveness, indicating the robustness of the modified biochar in multi-component solutions.

Regeneration experiments revealed that biochar could be effectively regenerated using 0.1M NaOH, recovering about 57% of the adsorbed phosphate, making it a sustainable and cost-effective option for repeated use.

In conclusion, the modified biochar derived from Acacia tortilis prunings, enhanced with iron and magnesium oxides, presents a highly effective method for removing phosphate from water. Its rapid adsorption rate, high capacity, and potential for regeneration make it a promising solution for mitigating phosphate pollution and recycling this vital nutrient from wastewater.