Alkaline leaching of low zinc content iron-bearing sludges

Abstract

Various types of waste materials containing zinc (e.g. dusts and sludges from gas dedusting process) are obtained in steel industry. The contents of Zn in these materials may vary considerably. Even a low concentration of zinc in recirculated products precludes their recycling in ferrous metallurgy aggregates. Long storage of this type of material can lead to contamination of soil and water by zinc compounds which can be leached out by acid rain, for example. This paper focuses on research involving alkaline leaching tests of low zinc content iron-bearing materials. These tests were preceded by the analysis of the elemental, phase and grain size composition, and analysis of the thermodynamic conditions of the leaching process. The main aim of research was to decrease the content of the zinc in the sludge to the level where it is suitable as an iron-bearing material for iron production (∼1% Zn). Leaching at elevated temperatures (368 K, 60 min) has led to a decrease in the zinc content in the sludge of about 66%. The research revealed that long hour leaching (298 K, 100 hours) carried out at ambient temperatures caused a reduction in zinc content by 60% to the value of 1.15-1.2% Zn.