Gasification Behavior of Phosphorus during Pre-reduction Sintering of Medium-high Phosphorus Iron Ore

Abstract

The effects of dephosphorization agents (SiO 2 , Na 2 CO 3 and Al 2 O 3 ) and reduction time on phosphorus gasification during pre-reduction sintering gasification dephosphorization were studied. The results indicate that the dephosphorization rate of apatite by carbothermal reduction is 23%, the dephosphorization rate of adding SiO 2 and Al 2 O 3 is 25%, and the optimal dephosphorization rate is 36% by adding SiO 2 and Na 2 CO 3 . The dephosphorization rate increased from 13% to 31% with the reduction time increased from 20 min to 60 min. Thermodynamic analysis shows that the promotion effect of Na 2 CO 3 on apatite reduction is stronger than that of Al 2 O 3 , and the thermodynamic conditions of apatite reduction are optimized to the greatest extent by adding SiO 2 and Na 2 CO 3 , with the starting temperature of carbothermal reduction of apatite decreased from 1 464°C to 746°C. P and C have the same variation and change trend, and the migration of phosphorus ito metallic iron is related to the carburizing reaction. The good heat storage of the sinter layer in pre-reduction sintering increases the time for maintaining the apatite reaction temperature and promotes the occurrence of dephosphorization reaction, however part of the phosphorus gas is absorbed by liquid metallic iron to form stable iron phosphorus compounds,which leads to the decrease of dephosphorization rate. Besides addition of dephosphorization agent, restricting migration of phosphorus into iron phase is the key point to increase gasification dephosphorization efficiency in sintering process.

Gasification Behavior of Phosphorus during Biomass Sintering of High-phosphorus Iron Ore

“…The multi-point sampling before and after roasting was used to detect the phosphorus content, and the dephosphorization rate was calculated according to the following formula. 16) η = 1 100 Where η represents the dephosphorization rate. P 0 and P 1 represent the content of phosphorus in the tablet before and after reduction, respectively.…”

“…Compared with the reduction temperature of apatite, the reduction temperature of iron oxide was lower, and the phosphorus gas volatilized in the reduction process was easy to combine with iron to generate Fe x P, which inhibits the gasification removal of phosphorus. 16) The larger pore diameter and higher porosity in the reduced sample were beneficial to the volatilization of phosphorus gas into the flue gas, thus increasing the dephosphorization rate. Compared with full coke breeze, the sample with biochar had a larger pore size and specific surface area after reduction, the distribution of internal voids was numerous and uniform.…”

“…Thereby, based on the sintering characteristics, it is of great significance to take measures to reduce the reduction temperature of apatite and make the reduced phosphorus gas volatilize into the flue gas under the action of sintering negative pressure. 16) Zhang 17) had carried out exploratory experiments on small pellet sintering dephosphorization and microwave sintering dephosphorization process. The results showed that the optimal dephosphorization rate was conducted with 5 mass% carbon mixing proportion, 0.75 mass% SiO 2 and 1.5% mass% CaCl 2 , and the corresponding dephosphorization was 25.71%.…”

“…When adding SiO 2 and Na 2 CO 3 , the reaction temperature of apatite decreased, which promoted the reduction reaction to generate phosphorus-containing gas. 16) In addition, CaO, SiO 2 , Al 2 O 3 , and Na 2 CO 3 interacted to form Na 2 CaSi 5 O 12 and NaAlSiO 4 phases with a low melting point. The formation of low melting point compounds improved the fluidity of the system and destroyed the inclusion structure of gangue relative to apatite in the ore, therefore the reduction reaction of apatite proceeded better.…”

“…Because Fe 2 P and Fe 3 C had a similar crystal structure, the phosphorus gas generated during reduction entered the Fe 3 C lattice to form Fe 2 P, consequently the phosphorus content in the iron phase was improved as a result of the increase of carbon content. 16)…”