Modification of Hardwood Derived Biochar to Improve Phosphorus Adsorption

The excessive application of phosphorus in agricultural lands leads to serious environmental issues. Efficient application is beneficial from an economic and environmental perspectives. Biochar can be used as a carrier for slow release of phosphate. However, its adsorption capacity is limited. In this work, biochar was prepared at different pyrolysis temperatures (350-550 degrees C). The biochar prepared at 550 degrees C had the highest adsorption capacity and was selected for modification by magnesium impregnation. Magnesium modification enhanced the adsorption capacity by 34% to a theoretical max adsorption capacity of 463.5 mg center dot g(-1). The adsorbed phosphate can be desorbed. The desorption was bi-phasic with fast- and slow-release fractions. The distribution of the phosphate fractions was pH dependent with slow release being most prominent in neutral conditions. Mg modified biochar can be used to recover phosphate and then used as a carrier for slow release of phosphate. The bi-phasic desorption behaviour is useful as the fast release fraction can provide the immediate phosphate needed during plant establishment, while the slow-release fraction maintains steady supply over extended periods.

Automated summary

Biochar prepared at 550 degrees Celsius had the highest adsorption capacity and was further enhanced by magnesium impregnation to reach a theoretical maximum adsorption capacity of 463.5 mg center dot g(-1). The bi-phasic desorption behavior of magnesium-modified biochar is useful for providing immediate phosphate needed during plant establishment, while maintaining a steady supply over extended periods.