Abstract:
Heavy metals pollution of water poses a major environmental challenge due to its
antagonistic effects. They are not biodegraded and tend to accumulate in human body
to toxic levels linked to some health effects. Therefore, there is need for their removal
in water. Technologies that exist such as membrane filtration are limited by their high
operation cost. However, adsorption is a cheap, efficient, and easy technique of
removal of pollutants from wastewater. There is limited information available on value
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addition of plastic waste for application as adsorbents. Application of modified
polypropylene plastic waste was explored in this study for remediation of Cd2+ and
Cr3+ ions from model solution. This was achieved by first chemically modifying the
plastic by use of hydrogen peroxide and hydrochloric acid to create adsorption sites.
The chemically modified plastic waste was characterized using Scanning Electron
Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The images
obtained confirmed availability of pores in the adsorbent which are critical for Cd2+ and
Cr3+ ions adsorption. The FTIR results confirmed the presence of hydroxyl groups on
the adsorbent which are vital for adsorption. Effect of adsorbent dosage, contact time,
solution pH and initial metal ion concentration were investigated and the concentration
of the resulting filtrate after adsorption determined using Inductively Coupled Plasma
Atomic Emission Spectroscopy (ICP-AES). The results from optimization experiments
showed that Cd2+ and Cr3+ ions adsorption was optimal at initial metal ion
concentration of 15 mg/L and 20 mg/L respectively, contact time of 45 mins and 60
mins respectively and optimum adsorbent mass of 0.1 g. Optimal pH values of 4.5 and
5.5 respectively were also observed. Equilibrium experimental results showed
adsorption capacities of 7.395 mg/g (Cd2+) and 6.225 mg/g (Cr3+) for Langmuir
isotherm model with R2˃0.99 indicating chemisorption process. This study shows the
good performance of the modified plastic waste in adsorbing the metal ions and also
value addition for the plastic waste. Polypropylene plastic waste can therefore be
applied in wastewater treatment to bring the concentration levels of heavy metals to
the required limits.
