Preliminary evaluation of galvanic sludge immobilization in clay-based matrix as an environmentally safe process

Abstract

This study attempts to determine the possibilities and limitations of the immobilization of galvanic wastes by their incorporation into clay-based materials. It focuses on the effects of several processing parameters such as the temperature of thermal treatment, the relative amount of sludge, and the physico-chemical aspects of the sample, on the fixing level of relevant metals (Zn, Ni, Fe, Mn, Pb, Cu, Cr) in thermally treated clay-based samples. The effectiveness of sludge inactivation was assessed by water-leaching test and conductivity measurements. In view of the potential use of the sludge stabilization products as construction materials, the linear shrinkage and bending strain of the fired samples was investigated. To characterize their morphology, mineralogy and composition, fired samples of clay and its mixtures with galvanic sludge were studied on a scanning electron microscope (SEM) coupled with an energy dispersive X-ray analyser (EDS) and X-ray diffractometer (XRD). It was found that the efficiency of metal immobilization is dependent on the clay composition and the temperature of the thermal treatment of the prepared mixtures. The thermal treatment of all samples at all temperatures resulted in the stabilization of all heavy metal ions (copper, nickel, iron, lead, manganese and zinc) with the exception of chromium.

Keywords:

• Clay
• electroplating sludge
• hazardous sludge
• leaching test
• thermal inactivation

Acknowledgment

The authors acknowledge the financial support of the Ministry of Science and Environmental Protection of the Republic of Serbia in the frame of projects No. TR 6867B and No. ON 142058.

Notes

* show deviations from USEPA RL (Regulatory Level; values—5.0 mg L⁻¹ for chromium (USA, Code of Federal Regulations) 40CFR261.24), and italicized values exceed the concentration limit used to define the hazardous nature of leachates, according to European Council Decision 2003/33/EC (0.1–0.5 mg L⁻¹).