Microstructure and formation kinetics of a freeze lining in an industrial copper FSF slag

Abstract

The freeze lining of an industrial copper flash smelting furnace slag, its growth kinetics and microstructure have been studied using a water cooled probe technique in a rotating crucible furnace at 1350uC. The first layers of iron silicate slag solidify on the water cooled metal surface as amorphous or glassy material with a minor fraction of crystalline spinel phase precipitated. At a distance of 4-5 mm from the cold face about 50% of the structure is composed of crystalline olivine (fayalite) and spinel phases embedded in a glassy matrix. Major thickness of the freeze lining is formed within first 15 min of slag contact with a cooled metal surface. The solidified microstructures obtained were compared with equilibrium phase assemblages calculated. The equilibrium solidification in the near solidus reactions includes the formation of pyroxene and rhodonite type phases, but they were not identified in the lining microstructures.

Freeze-lining Formation and Microstructure in a Direct-to-blister Flash Smelting Slag

“…3 shows a selected panorama over the well developed freeze lining micro structure formed on the cold finger over a relative long contact time of 40 min, covering about half of the whole lining thickness formed in the experiment. The mineralogical structure of the freeze lining is very different when compared with the matte smelting slag freeze linings studied earlier [17], due to two reasons: firstly, the conditions in direct-to-blister furnace, where metallic, sulphur-lean blister copper is stable, and secondly, the chemistry of feed mixture gangue of the smelter. It differs from most copper concentrates, in particular as to its concentrations of alumina as well as magnesia.…”

“…The chemistry of precipitated magnetite (spinel) differs significantly from that in the traditional matte smelting freeze linings [17]: it contains a high (>5%) concentration of copper, dissolved as oxide, Fig. 6, and occasionally cobalt which is typical minority component of the concentrates used at the smelter.…”

“…A detailed description of the experimental furnace and its instrumentation has been given elsewhere [17], but since the previous research series with copper matte making slags, four PT100 A class temperature sensors were inserted in the water cooled probe close to the slag surface. They are used for measuring heat flux to the cooling water within the slag bath.…”

Understanding Slag Freeze Linings

“…31,[43][44][45][46][47][48] Accurate in situ measurements of temperature profiles and deposit microstructures formed in operating smelters cannot be undertaken; however, it is possible to form these deposits in laboratory-controlled conditions using a cold finger technique. In this approach, the slag bath is held at constant temperature and a cooled probe is immersed in the bath.…”

“…The majority of these studies have focused on the phase assemblages and microstructures formed during the growth of the deposits. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] EXPERIMENTAL RESULTS…”