Preparation of manganese oxide coated coal fly ash adsorbent for the removal of lead and reuse for latent fingerprint detection

Heavy metals are becoming a huge problem in the environment and lead is one of them. Lead is disposed into water systems from huge industries such as paint industry, mining, and electroplating. In this study, manganese oxide coated fly ash (MnO₂-CFA) was synthesized and characterized. The BET surface area of CFA MnO₂-CFA was 18.4196 m²/g, 3 times more than the raw CFA (5.9231 m²/g). Batch adsorption experiments indicated that the uptake of Pb²⁺ fitted well in a Elovich kinetics model while the adsorption isotherm best fitted the Langmuir model with a maximum adsorption capacity of 141 mg/g at 40 °C and a pH of 7. Thermodynamic parameters obtained proved that the adsorption of Pb²⁺ ions using the MnO₂-CFA was endothermic and spontaneous. Furthermore, the adsorbent was highly selective towards Pb²⁺ in the presence of Mn²⁺, Zn², Ni²⁺and Cd²⁺. The Pb²⁺ removal % from a real water sample spiked with 30 mg/L Pb²⁺ was found to be 83.33%. The spent adsorbent was further applied in latent fingerprint detection which showed that Pb²⁺-MnO₂-CFA produced clearer latent finger print (LFP) images compared to MnO₂-CFA. LFP images were still clear 8 days after application of the spent adsorbent, proving that Pb²⁺-MnO₂-CFA is a promising labelling agent.