Abstract
Heavy metals are posing problems in the environment and one of them is lead. The disposal of lead into our water systems comes from industries such as the paint, mining, and electroplating industries. When water contains high concentrations of lead it causes severe health problems such as respiratory problems, liver damage and cancer. Various methods have been investigated for the removal of lead and adsorption is one of the popular and most suitable methods due to its advantages. In this study, candle soot was functionalised with HNO3 to enhance the adsorption capacity using a refluxing method and was applied in the adsorption of Pb2+ ions from aqueous solution.
The adsorbent (CNPs) functional groups were determine by using Fourier Transform Infrared Spectroscopy (FTIR), the crystallinity was determined using X-ray Diffraction (XRD), Brunauer Emmett and Teller (BET) was used to determine the surface area, Thermogravimetric Analysis (TGA), Scanning Electron Spectroscopy-Energy-dispersive X-ray (SEM-EDS) and Transmission Emission Microscopy were used to determine the morphology and The functionalisation of candle soot was confirmed by FTIR. This included a broad peak which was observed at 3450 cm-1 and showed that OH groups were present. FTIR studies after adsorption also confirmed interactions between Pb and this functional groups. The surface area which was verified by BET showed that there was an increase in surface area when pristine candle soot was modified to CNPs. Candle soot had a surface area of 135.52 m2/g and CNPs has a surface area of 174.19 m2/g.
Batch adsorption studies were carried out using CNPs as the adsorbent. The following parameters were optimized, contact time, pH, dosage, initial concentration of Pb2+ ions and temperature. At pH 8, Pb2+ had the highest percentage removal which was 99.2%. The adsorption data was fitted to Langmuir and Freundlich isotherm models and the Langmuir isotherm model was the more suitable one according to the data obtained. The maximum adsorption capacity was found to be 67.98 mg/g at 250C which is much higher than the other modified adsorbents reported in previous studies. The process of adsorption was an endothermic and spontaneous process. Based on the results of the coexisting ions study, CNPs were found to adsorb other cations but still had a high selectivity for Pb2+ in the presence of other metal cations. Real water analysis was also carried out, and it was found that the removal efficiency for Pb was 93.60% which also indicated that the adsorbent was effective for real water samples containing other pollutants.
After adsorption, to avert secondary pollution in the environment, the lead-loaded adsorbent was then implemented in cement production. The results obtained from cement production images displayed that Pb2+-CNPs can be a promising material to be used for cement production, if only higher percentages can be used (1.2%).