Leaching of water-granulated iron silicate slags and their compounds : A study of synthetic and industrial slag systems

• Copper smelter slag is a residue product of the pyrometallurgical extraction of copper. Due to its physical properties, the iron silicate type of copper smelter slag has many possible application areas, e.g., different aggregates and abrasives. During the copper-making process, some copper becomes distributed in the slag; therefore, copper recovery from the slag is commonly done through slag treatment processes. Despite treatment, copper-containing inclusions can remain in the final slag. In order to secure the environmental properties of slags containing inclusions, the leaching mechanisms needs to be understood, which is the focus of the thesis presented.Synthetic and industrial iron silicate slags have been studied with respect to the impact of the slag constituent’s oxide (glass), sulfide (matte) and metalloids (speiss) on leaching as well as the impact of chemical composition (ZnO and CaO content). The synthetic slags are melted in laboratory furnaces. The industrial slags have undergone a Zn-fuming and settling process (including CaO additions for some slags) to recycle and reduce the zinc content and further separate copper-containing inclusions such as sulfide (matte) and metalloid (speiss) species. The materials investigated in the thesis are solidified using water granulation.All materials are characterized by their chemical compositions and mineralogy. Further, industrial slag constituents are investigated regarding their leaching contribution. Syntheticiron silicate (oxide) is investigated regarding the influence of ZnO content and granulation temperature on Zn leaching. CaO-modified industrial iron silicate slags are investigated regarding the leaching of specific elements (e.g., Cu, Zn, Ni, As, Sb). The leaching tests examine the effect of pH, oxidation and time using water leaching, acid and oxidating leaching and dynamic leaching methods.Characterizing the slag constituents shows that the glass mainly contains amorphous iron silicate. The matte contains mainly copper sulfides, and speiss contains copper metalloids. The leaching results show that the glass contributes to Cu and Zn leaching at pH 8.4, and the speiss contributes to Ni and Sb leaching at pH 7.8. Further, the leaching contribution of matte and speiss increased with decreasing pH. The main leaching elements from the matte and speiss include Cu, Ni, As and Sb.Characterization of the ZnO-modified iron silicate shows that Zn is mainly distributed in glass and partly in fayalite. Further, the Zn leaching increases with granulation temperature, ZnO content in the glass and decreasing pH.Characterization of CaO-modified slags shows that up to 20 wt.% CaO dissolves into the glass phase. An increased CaO content resulted in increased Ca leaching, yielding higher pH. Leaching of Zn, Cu, Ni and Sb was on the other hand shown to decrease. Further, long-term leaching studies confirm increasing pH and Ca leaching. In contrast, the leaching of Cu, Zn and Ni showed a peak after a certain time, which was lowered with increasing CaO content in the slags. The leaching of As and Sb increased with increasing leaching time, but the increase diminished with increasing CaO content in the slags. A lower pH and an oxidating environment increased the leaching of Zn, Cu and Ni.The summarized results from this thesis indicate that the glass contributes to Zn leaching while copper-containing inclusions matte and speiss contribute to the leaching of Cu, Ni, As and Sb. The leaching of elements from the copper-containing inclusions matte and speiss can be limited by ensuring a pH buffer preventing acidification, for example, by CaO modification. CaO modifications decrease the slag leaching resistance, which contributes to increasing pH in the leachate by Ca-dissolution and hence decreased leaching of copper-containing inclusions in the slag. Also, the Zn leaching from the slag decreased with increasing pH in the leachate.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Process Metallurgy

Processmetallurgi

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