Mechanical and reduction characteristics of cold-pressed copper slag pellets composited within biomass and lignite

As a new reducer, biomass was tested as an alternative to coal in copper slag pelleting process by cold pressed preparation method. As two kinds of reducer, biomass and lignite were used in this paper. Without binder addition, the compressive strength of lignite pellets remained in the range of 44 N–75 N under experimental conditions. Compared with lignite, biomass provided higher reduction ratio and higher compressive strength. Fiber structure of biomass increased surface area and strengthened adhesive force of composite pellets. Compressive strength of biomass composite pellet was much higher than lignite composite pellets and remained steady between 2093N and 2246 N with the variation of pressure and CaO addition ratio when C/O was 1.0. Using biomass as reducer, reduction mechanism of copper slag was established. The reduction experiments showed that in the reduction reaction process, metallic iron outflowed from cracks in pellet and it was in the formation of sphere under the effect of surface tension. And the ‘sweating metallic iron’ reduced by biomass distributed more homogeneously than by lignite. When the temperature was above 1423 K, reduction ratio of copper slag was higher than 0.9. And reduction ratio reached a peak when CaO addition ratio was 0.3.