Surface modification can improve biochar adsorption capacity. Biochars were produced from wheat straw through low-temperature pyrolysis at approximately 450°C, activated with hydrochloric acid (HCl), and coated with iron (FeCl₃ 6H₂O) of different amounts. Results showed that activation with HCl and coating with iron can significantly increase biochar adsorption capacity. The increase after HCl treatment was very small at a high ratio of iron to biochar. The optimal ratio of iron to biochar for iron-coated biochar was 0.70. Adsorption capacity was calculated based on the amount of pure nitrogen or phosphorus. The maximum adsorption capacities were 2.47 and 16.58 mg g⁻¹. The most effective pH values for nitrate and phosphate removal were 3 and 6, respectively. The active substance of the optimal-modified biochar (OMB) was amorphous FeOOH, and the structure was the hydroxylated mineral surface of OMB in a water solution. The equilibrium pH of the adsorption solution was lower than 7 even when the initial pH of the solution was 11 because changed into , , and H₃O⁺ with the increase in pH. Adsorption experiments showed that OMB can be utilized to remove nitrate and phosphate from water.

A soil remediation method based on magnetic beneficiation is reported. A new magnetic solid chelator powder, FS@IDA (core-shell Fe₃O₄@SiO₂ nanoparticles coated with iminodiacetic acid chelators), was used as a reactive magnetic carrier to selectively capture non-magnetic heavy metals in soil by chelation and removal by magnetic separation. FS@IDA was prepared via inorganic-organic and organic synthesis reactions that generated chelating groups on the surface of magnetic, multi-core, core-shell Fe₃O₄@SiO₂ (FS) nanoparticles. These reactions used a silane coupling agent and sodium chloroacetate. The results show that FS@IDA could chelate the heavy metal component of Cd, Zn, Pb, Cu and Ni carbonates, lead sulfate and lead chloride in water-insoluble salt systems. The resulting FS@IDA-Cd and FS@IDA-Pb chelates could be magnetically separated, resulting in removal rates of approximately 84.9% and 72.2% for Cd and Pb, respectively. FS@IDA could not remove the residual heavy metals and those bound to organic matter in the soil. FS@IDA did not significantly alter the chemical composition of the soil, and it allowed for fast chelating capture, simple magnetic separation and facilitated heavy metal elution. FS@IDA could also be easily prepared and reprocessed.