Solution chemistry effects on orthophosphate adsorption by cationized solid wood residues

Area of Science:

• Environmental Chemistry
• Materials Science
• Water Treatment

Background:

• Orthophosphate (PO4^3-) is a key nutrient in aquatic systems, and its removal is crucial for mitigating eutrophication.
• Solid wood residues are abundant lignocellulosic materials with potential for environmental remediation applications.
• Cationization enhances the anion exchange capacity of biomass, making it suitable for adsorbing anionic pollutants.

Purpose of the Study:

• To characterize the adsorption of orthophosphate anions onto cationized milled solid wood residues.
• To investigate the influence of various parameters (pH, ionic strength, competing anions, time) on orthophosphate adsorption.
• To determine the adsorption capacity and binding energy of cationized wood and bark for orthophosphate.

Main Methods:

• Batch adsorption experiments were conducted using cationized milled wood and bark residues.
• Orthophosphate adsorption was studied as a function of sorbate-to-sorbent ratio, pH, ionic strength, and reaction time.
• The effect of competing anions (sulfate and nitrate) on orthophosphate removal was evaluated.
• Sorption data were fitted using the two-site Langmuir adsorption model.

Main Results:

• Adsorption isotherms indicated two types of adsorption sites with high and low binding affinities for orthophosphate.
• Cationized bark exhibited higher sorption capacity (0.47 mmol P/g) and binding energy (295.7 L/mmol) than cationized wood (0.27 mmol P/g and 61.4 L/mmol).
• Sorption capacity and binding energy decreased with increasing ionic strength due to competition from chloride ions.
• pH significantly affected sorption, with optimal removal influenced by the surface charge of cationized bark (pHzpc = 7.9) and orthophosphate speciation.
• Equilibrium was reached within 3 hours, and significant removal of orthophosphate by sulfate and nitrate required high molar ratios of competing anions.

Conclusions:

• Cationized milled solid wood residues, particularly bark, are effective adsorbents for orthophosphate removal from aqueous solutions.
• The adsorption mechanism involves ion exchange and Lewis acid-base interactions, supported by the influence of pH, ionic strength, and competing anions.
• These findings highlight the potential of cationized wood residues as a sustainable and cost-effective material for phosphate remediation.