Abstract
Water is known as a vital resource. Research institutions, industries and governments worldwide are challenged by emerging heavy metal ions (zinc, lead, copper, chromium) responsible for water pollution. The pollution of water by these heavy metals is a result of their release through mining activities, chemical manufacturing and industrial plants. The presence in water of heavy metals such as lead and zinc, even in small quantities, may cause significant concern due to their carcinogenicity and toxicity to several systems of the human body. For example, the treatment of zinc (or lead) targets several physiological processes, especially the ones that are related to immune response, cellular function, and skin health. Zinc treatment typically targets multiple sources of waste for its treatment, industrial wastewater generated from processes in metal, galvanizing, and electroplating finishing industries is the source targeted for an effective and recovery processes to manage zinc from waste. The aim of this project was to develop an elementary, cost-effective system for removing metal ions from water. Multiwalled carbon nanotubes (MWCNTs) were functionalised via a process with multiple phosphorylation agents. MWCNTs were functionalised with an acidic functional group to obtain oxidised MWCNTs. Then, via chemical modification of carboxyl groups introduced on the oxidised MWCNT surface, phosphorylated multiwalled carbon nanotube polymers (p-MWCNTs) were produced. The adsorbents were characterised using various techniques including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman, energy X-ray dispersive spectroscopy (EDX), Zeta potential, Brunauer-Emmett-Teller (BET) and ultraviolet-visible (UV-vis). Lead (Pb2+) and zinc (Zn2+) ions were recovered from an aqueous solution using phosphorylated MWCNTs. In the batch adsorption studies, other adsorbents such as pristine and oxidised MWCNTs were comparatively used with p-MWCNTs. The effect of multiple conditions such as concentration, the pH solution, temperature effect, adsorption time, precipitation and adsorption isotherms on lead and zinc uptake capacities were investigated.
FTIR spectra confirmed that polymerisation occurred when glutaryl chloride was added to the mixture of amino-phosphorylated MWCNTs. The adsorption results also revealed that the best concentration of 40 ppm was recovered with polymer MWCNTs for both lead
and zinc. Pb2+ and Zn2+ adsorption was principally pH-dependent, with maximum adsorption at pH 12 and 8, respectively. The adsorption isotherms were followed under 40 ppm initial concentration with Langmuir and Freundlich isotherms, showing that pollutants were adsorbed onto the homogeneous surface through monolayer formation.