Efficient removal of phosphate impurities in waste phosphogypsum for the production of cement

Area of Science:

• Materials Science
• Environmental Chemistry
• Industrial Waste Management

Background:

• Phosphogypsum (PG) is a significant industrial solid waste generated during phosphoric acid production.
• Environmental pollution concerns necessitate effective methods for PG waste utilization.
• Phosphate impurities in PG hinder its direct application in industries like cement manufacturing.

Purpose of the Study:

• To investigate the purification of phosphogypsum using oxalic acid (H2C2O4) for potential cement production.
• To determine the optimal concentration of H2C2O4 for effective phosphate impurity removal.
• To evaluate the impact of purified PG on cement properties and environmental implications.

Main Methods:

• Purification of phosphogypsum using varying concentrations of oxalic acid.
• Analysis of phosphate removal using differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence (XRF).
• Assessment of cement hydration properties and compressive strength using purified PG.

Main Results:

• Oxalic acid treatment effectively removes intercrystalline phosphate impurities by partially disrupting the gypsum crystal structure.
• Optimal purification achieved with 1% H2C2O4, removing 77.7% of phosphate impurities (as P2O5).
• The final setting time of cement using purified PG was reduced to 220 minutes, meeting national standards.
• Portland cement produced with 1% H2C2O4 treated PG exhibited comparable 3-day (20.8 MPa) and 28-day (44.6 MPa) compressive strengths.

Conclusions:

• Phosphogypsum purified with 1% oxalic acid is suitable for cement production.
• The H2C2O4 treatment offers a sustainable method for phosphogypsum utilization, significantly reducing environmental pollution.
• This approach provides a viable solution for managing industrial solid waste from phosphoric acid manufacturing.