Optimization of solidification/stabilization treatment of ferro-alloy waste products through factorial design

Abstract

Fine solid precipitates from lime neutralisation of liquid effluent streams from surface finishing operations in stainless-steel processing are treated by cement-based solidification. This process is examined using a modified factorial design technique, the Central Composite Rotational Design. The performance of these solidification/stabilization products was explored in terms of the effect of operational variables such as water-to-solids ratio, cement content and curing time which are deemed to be relevant in terms of engineering design practice. In particular, an attempt was made to quantify the interactions between those critical operational variables which dictate the suitability of the solidification method. Success criteria included leach resistance (for certain metal species) and mechanical strength of the composite products. It has been shown that the CCRD provides a rigorous account of solidified product behaviour and does so with a reduced requirement for a priori experimental testing. With the aid of this experimental design we have also shown an inverse relationship between strength and leach resistance of the critical constituents, here represented by chromium.