Cadmium immobilization in soil using phosphate modified biochar derived from wheat straw

Area of Science:

• Environmental Science
• Soil Science
• Materials Science

Background:

• Cadmium (Cd) contamination in soils poses significant environmental and health risks.
• Phosphate-modified biochar is a potential material for immobilizing heavy metals.
• Understanding the role of different phosphate species in biochar modification for Cd detoxification is crucial.

Purpose of the Study:

• To investigate the effect of different phosphate species (mono-potassium phosphate, dipotassium hydrogen phosphate, tripotassium phosphate) on biochar properties and Cd immobilization.
• To elucidate the Cd adsorption mechanisms on phosphate-modified biochar.
• To evaluate the efficiency of modified biochar in reducing bioavailable Cd in contaminated soil.

Main Methods:

• Pyrolysis of wheat straw impregnated with MKP, DKP, and TKP to create modified biochar.
• Biochar characterization (e.g., orthophosphate and pyrophosphate content).
• Batch adsorption experiments to determine Cd adsorption capacity and kinetics.
• Soil incubation tests using DTPA extraction to assess Cd bioavailability.
• Planar optodes technique to measure in situ soil pH changes.

Main Results:

• Cd immobilization efficiency followed the order: TKP-BC > DKP-BC > MKP-BC.
• TKP-BC exhibited the highest orthophosphate content, fastest adsorption rate, and largest Langmuir adsorption capacity (257.28 mg/g), 6.31 times higher than unmodified biochar.
• Precipitation of CdP minerals and cation exchange were the primary adsorption mechanisms.
• TKP-BC reduced soil Cd by 67.93%, significantly more than MKP-BC (18.41%) and DKP-BC (31.30%).
• TKP-BC demonstrated the longest-lasting effect in enhancing in situ soil pH.

Conclusions:

• Tripotassium phosphate modification significantly enhances biochar's capacity for cadmium immobilization in soils.
• Phosphate species composition critically influences biochar's performance in heavy metal remediation.
• Phosphate-modified biochar, particularly TKP-BC, offers a promising green remediation strategy for cadmium-contaminated soils.