Daneel Geysen

Solidification/stabilisation of arsenic bearing fly ash from the metallurgical industry. Immobilisation mechanism of arsenic

When a fly ash waste material from a copper refining process containing large amounts of As2O3 is solidified using cement and lime, the arsenic concentration in the leachate can be lowered to ca. 5 mg/l in a saturated solution of Ca(OH)2. It is shown that the decrease of the concentration in the leachate, mainly of As(III), is due to the formation of insoluble CaHAsO3 in the leachate in the presence of Ca(OH)2. This method is compared with a method whereby use is made of oxidation of the waste before solidification to oxidise As(III) to As(V) using H2O2. The arsenic concentration in the leachate of the extraction test of an oxidised S/S sample was lowered to ca. 0.5 mg/l, a factor of 10 below the one for a non-oxidised sample. It is shown that the decrease of the concentration in the leachate mainly of As(V) is due to the formation of insoluble Ca3(AsO4)2 in the presence of Ca(OH)2. Extensive use was made of the speciation program MINTEQA2, to clarify the immobilisation of arsenic.

Methylalumoxane MCM‐41 as Support in the Co‐Oligomerization of Ethene and Propene with [{C2H4(1‐indenyl)2}Zr(CH3)2]

Superior to the homogeneous catalyst or physisorbed catalyst system is a system with the ansa-metallocene catalyst [{C2 H4 (1-ind)2 }Zr(CH3 )] on a support formed by covalently anchoring methylalumoxane (MAO) on the internal pore walls of MCM-41. This system is a highly active and shape-selective mesoporous host in the co-oligomerization [shown schematically in Equation (a)] of ethene and propene with ansa-metallocenes. TMA=trimethylaluminum, ind=indenyl.

Oligomerization of propene on an alumoxane-grafted MCM-41 host with bis(cyclopentadienyl)zirconium dimethyl (Cp2Zr(CH3)2)

The anchoring of alumoxane, synthesized by the in situ hydrolysis of trimethylaluminum, on the internal pore walls of a mesoporous MCM-41 support generates a highly active and selective host for bis(cyclopentadienyl)zirconium dimethyl (Cp2Zr(CH3)2) in the oligomerization of propene. The regioselective preference of the immobilized metallocene is preserved and a typical Flory–Schulz distribution for the propene oligomers is obtained.

Ferroalloy quality and steel cleanliness

Abstract Ferroalloys are added during secondary steelmaking to impart special properties to the steel. Depending upon the ferroalloy quality this may lead to the formation of inclusions. The present knowledge lacks in the exact content of the individual elements and the nature of inclusions dispersed in the ferroalloys. In order to broaden the knowledge concerning ferroalloy quality, eight different ferroalloys (i.e. FeMo, FeNb, HCFeMn, LCFeMn, FeTi70, FeTi35, FeSi75 and FeP) were characterised for their impurity content. The samples were investigated for chemical analysis (inductively coupled plasma atomic emission spectroscopy and Leco combustion technique) and microstructural analysis (SEM energy dispersive spectroscopy). These impurities are linked to the ferroalloy manufacturing route. The inclusions observed in the microstructure are in good agreement with the inclusions extracted by the dissolution technique. In the present manuscript, the possible influence of ferroalloy quality over steel cleanliness is evaluated in the context of the impurities extracted and observed in the ferroalloys.

Characterisation of copper slag in view of metal recovery

Abstract In this study, the copper bearing particle of a fayalitic copper slag was assessed using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and X-ray computed tomography (CT). The copper content of the slag was ∼0·87 wt-%. Copper in this slag was present as sulphidic droplets. The content and particle size distribution of the major sulphide phases (bornite, chalcopyrite and chalcocite/digenite) were quantified using QEMSCAN. The copper bearing particles had a wide particle size distribution from a few micrometres up to millimetre level. Large copper bearing particles (>100 μm) were composed mainly of bornite and chalcocite/digenite and tended to accumulate in the lower part of the slag layer. As characterised with CT, ∼70% of the copper value was present in these large copper bearing particles.

Characterization of Copper Slag

Copper slag can be treated as a secondary resource since it usually contains a substantial amount of copper and other valuable metals. Characterization of the slags to determine the expected metal recovery is essential for the design of separation flow sheets. In this study, the chemical and mineralogical composition of a copper slag from El Teniente, Chile were characterized. The copper content of the fayalite based slag is around 0.87 wt% which is higher than for certain copper ores. Copper exists as sulfides in the form of droplets in the slag. The content and particle size distribution of the major sulfide phases (bornite, chalcopyrite and chalcocite) were quantified using analytical scanning electron microscopy (QEMSCAN). The copper bearing particles have a wide particle size distribution from a few microns up to mm level. Large copper bearing particles (> 100 µm) are composed mainly of bornite and chalcocite and tend to accumulate in the lower part of the slag layer. As characterized with X-ray computed tomography (CT), around 70 volume% of copper value exist in these large copper bearing particles.

Characterization of landfilled stainless steel slags in view of metal recovery

The slag samples taken from landfill, which originated from different metallurgical processes, have been characterized in this study. The slags were categorized as electric arc furnace (EAF) slag, argon oxygen decarburization/metal refining process slag and vacuum oxygen decarburization slag based on chromium content and basicity. EAF slags have higher potential in metal recovery than the other two slags due to its higher iron and chromium contents. The size of the iron-chromium-nickel alloy particles varies from a few μm up to several cm. The recoveries of large metal particles and metal-spinel aggregates have potential to make the metal recovery from landfilled slags economically viable.