ABSTRACT
Pollution of water, especially in communities close to crude oil deposits and refineries, has created worldwide concerns because of the associated heavy metals, inter-alia, released to the environment which have adverse effects on the environment - human and aquatic life. Despite all the efforts of the refineries to curtail this, the inorganic pollutants were not sufficiently catered for. Analysis of the pollution loading of wastewater samples collected from the dewatering tanks in the tank farm of Kaduna Refining and Petrochemicals Company (KRPC) and at the point of discharge to the receiving river indicated concentrations of 0.04 mg/l of Ni, 0.225 mg/l Pb, 0.022 mg/l Cd and 1.823 mg/l Mn as against 0.01 mg/l, 0.01 mg/l, 0.003 mg/l and 0.2 mg/l standards, respectively, set by the National Environmental standard Regulatory and Enforcement Agency (NESREA). There was a consideration to use commercial Zeolite 4A, deriving from its high pore volume and adsorptive sites, but in order to reduce the cost of importation of the Zeolite 4A, a cheap and available local kaolin from Kankara village in Katsina State was used as a blend. The kaolin was processed to sodium base metakaolin using ion exchange techniques to insert sodium ion in the metakaolin structure. The sodium based metakaolin was blended in various proportions with Zeolite 4A to form matrices of Zeolites 4A and metakaolin. The mineralogical and chemical compositions of Zeolites 4A, metakaolin and Zeolites 4A–metakaolin matrices were investigated and analysed using X-ray Florescence (XRF), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM)-Energy Dispersive X - ray (EDX) and Brunauer, Emmett and Teller (BET). The metakaolinization was achieved under controlled calcination at the temperature of 750 oC for 3 hours and the blend of Zeolites 4A and metakaolin in the ratio of 25 to 75 % respectively gave a unique matrix. The batch adsorption process was used to investigate the effect of variables such as contact 7 time, matrix dose and pH, on the response. The aggregate removal of the specified heavy metals (nickel, lead, cadmium and manganese) from crude oil tank farm wastewater was achieved in one batch process. This could be attributed to the adsorbent’s high surface area per unit mass, numerous ionic sites per unit mass and their corresponding affinity to the metals. Isotherm and Kinetic studies were carried out. The correlation coefficient (R2) for the adsorption isotherm models showed that the experimental data fitted well with the Freundlich, Langmuir, Temkin, and pseudo – second – order models. A statistical analysis was also carried out for factorial and Response Surface methodology (RSM). The results indicated that the main effects and the 2-way-interactions of the three variables has the highest effect on the response and should be more carefully controlled during routine experiment. The RSM results indicated that at optimum condition of 1.28 g/50 ml of Matrix 4 dose, 20 minutes contact time and pH of 10.35, that the adsorption of 97.991 % nickel, 94.234 % lead, 99.239 % cadmium and 99.919 % manganese could be achieved which is commensurate to the one factor at a time laboratory result of 1 g/50 ml, contact time of 10 minutes and pH range of 8 - 10. The crude oil tank farm wastewater treated at this condition was compared to the untreated sample and it showed a marked decrease in the concentration of the specified metals far below the standard limits set by NESREA.
