Physical-Chemical Processing of LD-Slags

Ali Kamali Moaveni

Research output: ThesisDoctoral Thesis


The present research work investigates the physical separation techniques to reduce the phosphorus concentration of LD-Slags. LD-Slags contain about 25 % total iron, however, the presence of about 1 % of P2O5 represents a severe restriction for re-usage in the steelmaking process. Up to now, all efforts - by either magnetic sorting or froth flotation - did not result in an efficient separation process regarding the phosphorus and iron rich phases. Optical microscopy studies revealed the heavy and worm-shaped intergrowth texture of the co-existing phases due to the free-cooling (under air atmosphere) of the corresponding melt at the industrial site to be the reason for separation inefficiency. The raw material´s analysis including optical and scanning electron microscopy with energy-dispersive element spectroscopy (EDS) in property classes showed that the slag is constituted of free-lime, di-calcium silicate (C2S), metallic iron, Mg-wuestite and Ca /Al-ferrites in a wide range of elemental composition, while the phosphorus is hosted by the C2S phase. In order to allow the use of conventional separation techniques, a pre-conditioning stage was developed to alter the intergrowth pattern of the co-existing phases, making use of the hydraulic properties of the C2S phase. To accelerate the hydration the first process step is run in an autoclave using CO2 gas to increase the pressure at ambient temperature. As a result of the chemical reactions, the phosphorus bearing phase (C2S) is mobilized from the interior of the particles and precipitated at the surface of the grains in the form of calcium carbonate and silica phases. The new arrangement of the phases provides higher accessibility of the phosphorus bearing components. After mechanical treatment, predominated by frictional forces, magnetic separation in a variety of field intensities was proved to be a selective technique to separate the phosphorus bearing diamagnetic phases from the para- to ferromagnetic oxides. The experimental results illustrated that using the available matrix separator at the laboratory of the Chair of Mineral Processing at 0.4 tesla background field intensity the optimum conditions regarding the recovery of iron and phosphorus to the magnetic product are achievable. The produced magnetic fraction carries 75 % of the total iron while the grade of P2O5 was reduced by half to 0.54 %.
Translated title of the contributionPhysikalisch-chemische Aufbereitung von LD-Schlacken
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Flachberger, Helmut, Assessor A (internal)
  • Harmuth, Harald, Assessor B (internal)
Publication statusPublished - 2019

Bibliographical note

embargoed until 25-06-2024


  • Physical separation
  • LD-Slag
  • Carbonation
  • Accelerated hydration

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