The Development and Evaluation of Analytical Procedures for the Determination of Heavy Metals in Industrial Effluents

Abstract

This project is concerned with the development and evaluation of an atom-trapping technique for determination of heavy metals in environmental samples. Modified atom-trapping technique using fabricated nickel tube/sample holder (crucible) was employed to increase the sensitivity of a flame atomic absorption spectrometry. Basic performance data for different parameters, such as burner height and the height of the support, were studied. Different designs and ways of placing the atom trap over the burner were evaluated to optimize the experimental conditions. The height of the tube’s support was varied, as well as, its design. The optimal position, for maximum light path through the tube, was obtained experimentally. Results of this attempt using nickel atom trap method on a number of standards of lead, cadmium, copper, zinc, cobalt, manganese and nickel concentrations, showed high sensitivity for the technique (1.2 - 4.1 fold) when compared to the conventional flame atomic absorption spectrometry. The improvement factors on the absorbance signals for the various metals were as follows: Cd =3.8 - 4.1; Pb = 1.8 - 2.2; Cu = 1.9 - 2.3; Mn = 1.2 - 1.7; Zn 2.3 - 2.5; Co = 1.2 - 1.8 and Ni = 1.6 - 2.1. These data indicated that a significant improvement in sensitivity has been achieved, using the nickel tube atom trap method. The results from this study suggested that the method, as an analytical procedure, is more sensitive than the conventional method for the determination of heavy metals in environmental samples. Thus a study was carried out to analyse effluents discharged from small and medium scale industries. These areNaraguta leather tanning effluents, Jos; Majema leather tanning effluents, Kano; a small-scale industry located at Sharada Industrial Estate Phase III leather tanning effluents, Kano; NASCO Group of Companies, Jos and Jos International Brewery (JIB), Jos. The results showed some pollution in these effluents for the various elements above the Interim Effluent Limitation Guidelines in Nigeria for all Categories of Industries. The Naraguta leather tanning had high value of zinc. The Majema leather tanning effluent is polluted with lead, copper, and zinc, while the Sharada leather tanning effluent had high zinc, with a very close value to the limit of copper. NASCO is polluted with copper, and zinc, as well as, Jos International Brewery (JIB).An attempt was made to increase sample volume from 0.2 ml to 2 ml by redesigning the nickel tube, accommodating more analyte reaching the flame. Analytical performance, such as sensitivity, precision, detection limit, and accuracy of the method, was carried out and the results compared with those from literature. One advantage of the developed nickel tube atom trap method is the very small sample solution requirement for analysis. Further more; its simplicity and low cost would be an advantage to many laboratories with limited resources. The interference study of NaCl on the absorbance of lead was carried out. The result showed that NaCl exhibited a significant level of suppression at 5mg/L of Pb (i.e. 1.17% at 10% NaCl to 1.28% at 30% NaCl reduction in absorbance signal).