Palygorskite for the uptake and removal of pharmaceuticals for wastewater treatment

• Ranitidine (RT) uptake on palygorskite (PA) followed Langmuir isotherm to 156 mmol/kg.
• Uptake of RT on PA was limited only to the external surfaces of PA.
• Cation exchange was mainly responsible for RT uptake when pH < pKa.
• 2,5-Disubstituted furan group interacted with the PA surface via a delocalized π-bond.
• The high affinity of RT on PA suggests PA being a good sorbent for wastewater treatment.

In this study, ranitidine (RT), a cationic drug was tested for its removal by palygorskite (PA) under different physico-chemical conditions, such as initial RT concentrations, contact time, equilibrium solution pH, ionic strength, and temperature. FTIR, SEM, and XRD analyses were conducted to determine the mechanisms of RT uptake on PA. The results showed that cation exchange or electrostatic interactions between the negatively charged PA surfaces and positively charge dimethylamine of RT was the major mechanism of RT uptake when solution pH was less than the pKa value of RT. Under high pH conditions, the 2,5-disubstituted furan group interacted with the PA surface via a delocalized π-bond, suggesting that the RT molecules were parallel to PA surface. The larger values for the RT distribution coefficient between PA and solution via electrostatic or cation exchange interactions and delocalized π-bonds in a multi-regression analysis confirmed these mechanisms. The XRD results showed no expansion of the (1 1 0) reflection of PA while the SEM observation showed no changes in crystal size and morphology, indicating that the sites for RT uptake were limited to the external surfaces of PA.

The uptake of RT on PA was dominated by electrostatic interactions via cation exchange when solution pH was less than the pKa value. At high pH the 2,5-disubstituted furan group interacted with the PA surface via a delocalized π-bond, suggesting that the RT molecules were parallel to PA surface.Figure optionsDownload high-quality image (170 K)Download as PowerPoint slide