RECOVERY, RECYCLING AND REUSE OF STEEL FURNACE SLAG UNDER EGYPTIAN CONDITION

Abstract

This study concerned with the utilization of the electric arc furnace (EAF) steel slag which is a solid waste produced during crude steel manufacture. Steel furnace slag was being utilized in many countries all over the world in many applications. In Egypt, very small percentage of steel slag was being utilized although there are huge quantities of steel slag accumulated through the last years. The huge quantities of steel slag need vast areas for storage till utilization or safe disposal. Many facilities may follow unsafe and illegal steel slag disposal measurements which might pollute the environment.

This study aims to identify the suitability extent of utilization of Egyptian EAF steel slags in different applications, to identify its capacity to be comparable with natural aggregates in their properties, and to identify the appropriate applications of the EAF steel slag generated from Egyptian steel factories. The study contains results from laboratory physico – chemical and environmental behaviors investigations of the EAF steel slags samples from six different sources in Egypt. These investigations include: field observations; physical properties: shape, bulk density, water absorption, resistance to grinding and abrasion, liquidity, plasticity, and volume stability; the chemical characteristics; and the environmental behaviors. The results were compared with the requirements of national and/or international standards and regulations.

Absence of quality control strategy for generated EAF slags is observed through field studies, this appeared to be the most important obstacle in the direction of utilization of EAF steel slag of Egyptian steel factories under study. The physical properties are shown to be generally comparable and independent of their producers, comparable with those of natural aggregates and sometimes better than them and compatible with the specifications set for road-making materials. The percent of free CaO and MgO is very low or nil, which indicates the volume stability of the slag under study. The chemical compositions are generally comparable and independent of their producers. They are also comparable with European low MgO EAF steel slags and comprise of 35 – 53 % basic oxides, 21 – 6.5 % neutral oxides and 13 – 19 % acidic oxides. These compounds are generally similar to those found in the natural environment.

Based upon the results of environmental behaviors investigations, except for metals of Cr, V, and Al as well as the parameters of pH value and the electrical conductivity; the leaching of the other elements is insignificant. The release of these metals (Cr, V, and Al) and the values of these parameters (pH and electrical conductivity) are expected to increase in the long-term applied scale and associate with worse environmental impacts such as water and soil pollution and corrosion of Aluminum or galvanized steel pipes placed in direct contact with the slag. To address potential question regarding the safety of aimed future utilization of EAF slag under study, risk assessments study focusing on these parameters of interest was suggested. The mobility and toxicity of heavy metals strongly depend on their speciation, so study suggested establishment of a project that aims to predict the long-term release rates and mechanisms of V and Cr present in EAF slag as traces focusing on their speciation.

It is concluded that, after the suggested periodically insurance of the volume stability and environmental behaviors compatibility in the long-term applied scale through quality control strategy and systems, the properties of EAF slags under study qualify them as aggregates for high trafficked road layers, construction material and hydraulic engineering purposes.