Thermal properties and phosphate adsorption efficiency of coarse aluminum silicate fraction

Abstract

A clay deposit from Poskimäki (PM, Puolanka, Finland) was fractionated, and the coarse fraction (size 0.02–2 mm) was characterized to find potential applications in water or waste water treatment. The coarse fraction contained mainly quartz, kaolinite, and iron-containing compounds. Thermal behavior was investigated by simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC). The observations were supported by thermodynamic calculations executed with FactSage and HSC software and their databases. TGA–DSC analyses verified the differences between the untreated and annealed (800°C) samples. Kaolinite transformed into amorphous metakaolinite at 450–600°C. Phase transformations also occurred at a lower temperature range (240–320°C) with the PM sample. TGA–DSC data suggested the use of different annealing temperatures for the modification of the PM sample. The PM samples (non-annealed, 185, 360, 800°C) were tested as adsorbents for the removal of phosphate from water. The PM-a360 sample had the highest specific surface area and worked best in phosphate removal. The phosphate adsorption efficiency increased with decreasing pH.

Keywords:

• Iron oxide minerals
• Thermal properties
• Adsorption
• Phosphate

Acknowledgments

The authors would like to thank the Provincial Government of Oulu, the Council of the Oulu Region, the City of Oulu, the European Regional Development Fund, and the Academy of Finland for funding this research and Tuomo Pikkarainen from Morenia Ltd. for his inspiring discussions.