Removal of Phosphorus from LD Converter Slag by Floating Separation of Dicalcium Silicate during Solidification

Abstract

SynopsisMineralogical study of LD converter slag was carried out by means of microscopic and EPMA examinations and phosphorus was found to exist only in dicalcium silicate as solid solution. This led to the study of separation of dicalcium silicate from LD converter slag in order to remove phosphorus.When liquid slag was solidified slowly, most dicalcium silicate particles accumulated in the top part of the crucible and fewer in the bottom. The phenomena can be interpreted as follows; on solidification, dicalcium silicate is crystallized primarily and floats up owing to the difference of density between dicalcium silicate and residual liquid. By using this phenomena, we can separate LD converter slag into two layers, top and bottom in a vessel. As a result of slow cooling, CaO, Si02 and P205 are enriched in the top, and FeO, Fe203 and MnO in the bottom.Dicalcium silicate is apt to separate more efficiently with higher total iron content in slag, and at higher start temperature of cooling, close to liquidus temperature. The efficiency of separation was improved by blowing oxygen into the molten slag before cooling.

Recovery of Phosphorus from Dephosphorization Slag Produced by Duplex High Phosphorus Hot Metal Refining

“…18) Ono 3) suggested that when liquid BOF slag solidified slowly, most dicalcium silicate was crystallized primarily and accumulated in the top part of slags. CaO, SiO 2 and P 2 O 5 were enriched in the top, while FeO, Fe 2 O 3 and MnO in the bottom.…”

“…Ono et al 3) developed a method for removal of phosphorus by floating separation of dicalcium silicate during slow solidification. Li et al 4) proposed a slag regeneration process to reduce the BOF slag in an iron bath furnace, and then the high phosphorus hot metal obtained from the reduction process was dephosphorized to get high P2O5 content slag for the use of fertilizer.…”

Leaching Dicalcium Silicates from Iron Ore Sinter to Remove Phosphorus and Other Contaminants.

“…In addition, leaching results indicated that the C 2 S in the testwork sinter was also enriched in Cr and K with respect to the bulk composition. Many researchers have investigated the substitutions of various components into C 2 S [39][40][41] and in the fields of iron and steelmaking there has been a particular focus on P [36][37][38] (because it is an undesirable contaminant). Some iron-making literature contains data for the partitioning of foreign components into C 2 S at low temperatures (down to ϳ1 300°C), 39) but the great majority of research to date has focused on high temperature molten metal/slag mixes and not C 2 S in ore agglomerates.…”

“…30,39) 3) C 2 S is known to incorporate a wide variety of impurities in several different systems, including those relevant to the cement industry [39][40][41] and steelmaking slags, where they preferentially concentrate undesirable components. [36][37][38] 4) The incorporation of impurities in the crystal lattice can stabilise different polymorphs of C 2 S and thereby inhibit phase transformations. 39,41) 5) At least one polymorph of C 2 S (b) is known to gelatinise in dilute HCl 42) and the hydration of C 2 S is well understood in the cement industry.…”

“…Cement manufacture, [30][31][32][33] magnesia refractory related research 34,35) and other parts of the iron and steelmaking process [36][37][38] either rely on, or are affected by, the properties of C 2 S and therefore an appreciable amount of research has been conducted into various aspects of these phases. A review of this literature on the C 2 S polymorphs reveals that some of the properties of this group of minerals are unique amongst sinter phases and this fact may potentially make them exploitable for the upgrading or further processing of sinters.…”