Preparation and Physio–Chemical characterisation of activated carbon derived from prosopis juliflora stem for the removal of methylene blue dye and heavy metal containing textile industry effluent

Abstract

An experimental work endeavoured and presented in this article focuses on the removal of Methylene Blue (MB) dye and Heavy Metals (HM) such as lead and copper from textile industry effluent by the adsorption process with ZnCl2-activated carbon. Initially, carbon was prepared using the cheapest and environmentally hazardous precursor of Prosopis Juliflora plant (Stem) and called Prosopis Juliflora Stem Carbon (PJSC). Then the PJSC was chemically activated by impregnating ZnCl2 with a ratio of 1:0.5 at a temperature of 800 °C in muffle furnace about 1 h and named as ZnCl2-activated Prosopis Juliflora Stem Carbon (ZAPJSC). The physio–chemical characteristics such as yield, pH, conductivity, bulk density, moisture content, ash content, volatile matter, fixed carbon content, as well as solubility in acid and water were calculated. Surface textures of PJSC and ZAPJSC were characterised by Scanning Electron Microscopy (SEM); functional group characterisation was performed by Fourier Transform Infrared Spectroscopy (FTIR); elements in the adsorbents were identified by Energy Dispersive X-Ray Analysis (EDX); and Brunauer-Emmett-Teller (BET) surface area analysis was carried out to find the surface area, pore volume, and pore radius of the adsorbents. Surface area was found to be 252.730 m2/g which showed that ZAPJSC was having enormous bores meanwhile surface area of PJSC was 85.508 m2/g. In this context, the central composite design (CCD) approach-based response surface methodology (RSM) was performed to investigate and optimise the effects of process parameters on the adsorption of MB by ZAPJSC. The optimum level of process parameters such as contact time of 5.4 min and dosage of 85 mg were achieved with MB adsorption efficiency of 99.05%. Further, pseudo-first-order and pseudo-second-order models were used to fit the present experimental data. Pseudo-second-order rate equation was perfectly fit to provide a realistic description of adsorption kinetics. Equilibrium isotherms were investigated by Langmuir and Freundlich equations. Langmuir equation was found to best represent the equilibrium data for MB-ZAPJSC system. Thermodynamic study showed that the adsorption of MB on ZAPJSC (with a more negative Gibbs free energy value) was more favoured. Next, batch adsorption experiments for methylene blue dye and heavy metals (lead, copper, manganese, iron, cobalt) were carried out as parameters of effect of contact time and adsorbent dosage. Lastly, ZAPJSC adsorbent showed a reuse efficiency of 73.34% after four consecutive adsorption-desorption cycles in MB removal. These results indicate that the ZAPJSC could provide base for more low-cost activated carbon to be used as adsorbents for MB dye removal and heavy metals.