Valorization of rare earth processing byproducts for agriculture usage

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Sandy soils present agricultural challenges due to poor structure and low capacity.
• Soil conditioners can mitigate these issues, but their environmental impact requires careful evaluation.
• Phosphogypsum organic (PG organic) is a potential soil conditioner for sandy soils.

Purpose of the Study:

• To investigate the accumulation of metal ions and radionuclides in soil, water, and plants after applying PG organic to sandy soil.
• To assess the environmental safety of PG organic as a soil conditioner over 23 months and three cropping seasons.
• To evaluate the leaching potential of contaminants under simulated and field conditions.

Main Methods:

• Field application of PG organic to sandy soil over 23 months and three cropping seasons.
• Laboratory simulation using open leaching columns with varying pH leachants.
• Analysis of metal ions and radionuclides (²²⁶Ra, ²²⁸Ra, ⁴⁰K) in soil, water, and plant tissues.
• Calculation of biological accumulation coefficients, contamination factors, I-geo index, and pollution load index.

Main Results:

• Metal ion release from PG organic was higher at pH < 4.6 and significantly decreased at pH > 5.6.
• Measured metal ion levels in surface water, borehole water, and soil remained below drinking water standards.
• No significant accumulation of metal ions or radionuclides was observed in soil, plants, or water.
• Naturally occurring radionuclide concentrations in soil and plants were lower than previously reported averages.
• Under field conditions (pH > 5.6), PG organic showed reduced solubility, preventing radionuclide leaching into groundwater.

Conclusions:

• Application of PG organic to sandy soil poses no adverse impact on soil, plants, or water quality.
• PG organic is a safe and suitable soil conditioner for improving sandy texture soils.
• Environmental risks associated with metal ions and radionuclides are minimal under typical field application conditions.