Distribution of elements in slag, matte, and speiss during settling operation

Abstract: To cope with current trends in the base metals industry due to the lack of
pure mining resources, booming metals prices, and growing demand for base
metals: new thinking regarding the nature of metal resources as well as
novel recycling technologies is needed. Slags from base metals'
production can be a superior material for recycling. Currently, at the
Rönnskär smelter plant, copper slag is recycled in a continuous
procedure, including fuming, settling, and granulation. The main product is
called Iron Sand with smaller amounts of matte and speiss. These two phases
contain a considerable amount of Cu, Ni, and precious metals. Investigating
the distribution of elements and oxides in these separate phases and the
effect of CaO as a common impurity, is the main aim of this study.
The original materials, including settling slag, matte, and speiss, were
delivered by Boliden AB, Rönnskär Smelter Plant. Each material was dried,
crushed, milled, and separated in the mineral processing laboratory of
Luleå University of Technology for later analysis with X-ray
diffractometery (XRD) and thermal treatment. Six different samples were
prepared by homogenously mixing these three phases along with different
ratios of CaO. Then, the six samples were placed in alumina crucibles and
remelted in a Tamman furnace under N2 atmosphere at 1400°C for one hour to
attain maximum settling. After cooling, slag, matte, and speiss were
carefully separated from solidified material. A fraction of the materials
were mounted and prepared for light optical microscopy (LOM) and scanning
electron microscopy (SEM) investigations. The remaining material was
crushed and milled for X-ray diffractometery (XRD) and chemical analysis.
XRD analysis disclosed that the matte and speiss result in very complicated
patterns, which are not easily interpreted.
Treated samples along with original samples were sent to Rönnskär smelter
plant for accurate chemical analysis of Cu, Ni, Fe, Zn, Pb, Sn, Sb, As, Ag,
S, Al2O3, MgO, CaO, and Fe3O4. The results of XRD, LOM, SEM, Chemical
Composition, and Thermodynamic studies reveal that the distribution of
elements and components change with respect to CaO content. The results
have been extracted and tabulated in this thesis work. The higher the lime
content the greater the formation of Augite [Ca (Mg, Fe) Si2O6] in the slag
phase, whereas little or no affect was noticed on distribution of elements
in matte and speiss. Iron content in the speiss phase did decrease with
addition of lime into the system. Furthermore, it was determined that Ni
present in speiss mostly occurs with either As and Fe, or Sb and Cu.