Expanded Perlite for Cadmium and Lead Removal from Synthetic Rainwater: Adsorption Performance and Fixed-Bed Column Design
Lola Domnina Pestaño *
Chemical Engineering Department, Faculty of Engineering, University of Santo Tomas, Philippines and Research Center for the Natural and Applied Sciences, University of Santo Tomas, Philippines.
Eira Datul
Chemical Engineering Department, Faculty of Engineering, University of Santo Tomas, Philippines.
Jinessa Mary Surot
Chemical Engineering Department, Faculty of Engineering, University of Santo Tomas, Philippines.
Joshanne Mae Toledo
Chemical Engineering Department, Faculty of Engineering, University of Santo Tomas, Philippines.
*Author to whom correspondence should be addressed.
Abstract
Utilising the abundant rainfall in the Philippines as an alternative source of clean water is possible due to the low concentration of contaminants in rainwater (RW). However, the presence of heavy metals such as lead and cadmium may pose serious health risks to the users. To address this issue, various low-cost adsorbents have been studied and applied for the removal of heavy metals from water. In this study, the performance of a low-cost natural mineral adsorbent called expanded perlite (EP) in removing heavy metals was investigated. EP properties such as morphological structure and surface functional groups present were determined using Scanning Electron Microscope (SEM) and Fourier Transform Infrared spectroscopy (FTIR), respectively. Batch adsorption studies of cadmium and lead were conducted under different EP dosages and contact times. Synthetic RW was prepared by diluting heavy metal stock solutions to 1 mg/L per metal. Analysis of results was done by developing Langmuir, Freundlich and Dubinin-Radushkevich (DR) isotherm models, and Lagergren’s pseudo-first order and Ho’s pseudo-second order kinetic models. A fixed-bed column was designed for the adsorption of Cd (II) and Pb (II) from rainwater. Analysis showed the adsorption of heavy metals fit better with the Freundlich and DR isotherm model than the Langmuir, suggesting the adsorption is multilayer and physisorption, and the pseudo-second order kinetic model. The removal efficiency of EP for Cd (II) and Pb (II) were 85.8042% and 50.843%, respectively. The adsorption capacity of Cd (II) and Pb (II) was 19.4630 mg/g and 2.9818 mg/g, respectively. The study indicated that EP is significantly effective in the adsorption of cadmium and lead ions in RW. An adsorption column was designed using the breakthrough curve evaluation of the Thomas Model and by using batch data gathered from the experiments. A fixed bed column was designed for the adsorption of Cd (II) and Pb (II) with a height of adsorbent medium of 16.75 m. Using EP, heavy metals such as cadmium and lead can be efficiently removed from rainwater, supporting safe water use at the household and community levels.
Keywords: Expanded perlite, synthetic rainwater, batch adsorption, fixed-bed column, Langmuir isotherm model, Freundlich isotherm model