Dispersion Behavior of Blast Furnace Sludge for Valuable Metal Recovery

Blast furnace sludge, which comes from the iron making process, contains many valuable materials including iron, carbon, and zinc, etc. Because a cohesive agent is added during filtration, fine sludge particles are agglomerated together. Therefore, This makes it necessary to disperse the sludge in solution before separating or recovering valuable materials. In this study, the effects of solid/liquid (g/L) ratio, ultrasonic dispersion conditions, the pH of solvent, and the concentration of dispersant on the dispersion of sludge were investigated by measuring the interfacial properties (zeta potential and hydrodynamic size) of sludge particles. High absolute value of zeta potential and small hydrodynamic size suggests that the sludge particles in the solution presents good dispersion. The absolute value of zeta potential increased gradually at high solid/liquid ratio and ultrasonic dispersion intensity. But when the sludge in solution was dispersed for more than 30 minutes, the absolute value of the zeta potential decreased due to increasing contact and interaction between the particles. Optimal dispersion operations were conducted and when the pH of the solution was adjusted to 11, the zeta potential value was measured to be -44.8 mV. This means that the sludge formed the most stable dispersed phase. The lowest zeta potential was measured to be -46.4 mV with the addition of sodium hexametaphosphate (NaPO3)6 in the solution. It is thought that the sodium hexametaphosphate reduced ionic strength by removing alkali metal ions from the solution of sludge.

OXYFINES Technique for Upgrading Zinc Containing Blast Furnace Sludge—Part 2: System Analysis

Integrating novel technology in production systems for the upgrading and further use of residual materials is a potential way of improving the resource efficiency. Assessing technology integration prospects, by performing system analysis, assists in the forecasting of effects and opportunities for different concepts. Based on pilot trials results, using Linde’s OXYFINES technique for upgrading zinc containing blast furnace sludge, a system analysis was performed on the prospects of integrating an OXYFINES concept in an iron and steel production route. The calculations were made based on one option for a full-scale OXYFINES concept for indicating the effects on the blast furnace zinc load, raw material consumption, energy use and carbon dioxide emissions from using the OXYFINES sinter product as a raw material in blast furnace ironmaking or in the basic oxygen furnace steelmaking. The summarised system analysis results showed that the most advantageous metallurgical, environmental, and economic potential was realised in the calculations of using the sinter in the basic oxygen furnace. However, the sinter was found as well suitable for use in the blast furnace when considering mainly the metallurgical and the economic effects.

OXYFINES Technique for Upgrading Zinc Containing Blast Furnace Sludge—Part 1: Pilot Trials

In the Swedish steel industry, much work is put on further increasing the recycling and use of residual materials. However, blast furnace sludge is one residual which currently, despite its valuable contents of iron and carbon, is put on landfill or long-term storage due to its zinc content. Linde has developed the OXYFINES technique which is suitable for upgrading of fine particulate and zinc containing materials. The material is fed to the OXYFINES burner whereby its zinc content is vaporised to a generated dust phase whereas other non-gasifiable contents, such as iron, forms an oxidic sinter phase in the bottom of the reactor. The technique has proven a high degree of zinc separation, is relatively flexible and straightforward, and does not require sludge pre-treatment such as drying. Pilot set-up and trials, using the OXYFINES technique, were performed at Swerim’s research facility. In the trials, the effects from altering different process parameters were tested aiming to develop an optimal concept for upgrading the blast furnace sludge. The pilot trials’ results showed the required process settings to attain a high degree of zinc separation from the sludge, and to generate an iron oxide product, suitable for straightforward charging to the steelmaking process.

Effect of Metallurgical Waste Properties on Determining Suitable Recycling Method

Recycling of solid waste generated from metallurgical industries will avoid disposal of wastes, enhance the use of secondary raw material fines and save costs. Numerous hydrometallurgical and pyrometallurgical processes, or a combination of both, have been proposed for the utilization of metallurgical waste. Due to insufficient knowledge of the properties of these wastes, most of these attempts still have some technical difficulties. Investigation the properties of metallurgical waste is needed before choosing the suitable recycling process.The present work describes the chemical, morphological and mineralogical properties of blast furnace sludge (BFS) and basic oxygen furnace sludge (BOFS) produced in steel plants in Finland. The investigations indicated that BFS and BOFS show significant contents of iron and coke. The sludges also contain considerable concentrations of unwanted elements such as Zn. The authors propose that microwave dezincing followed by briquetting or pelletization represent a potential method for sludges recycling. Owing to high Fe and C content it can be utilized as self-reducing material.

Iron Recovery from Bauxite Tailings Red Mud by Thermal Reduction with Blast Furnace Sludge

More than 100 million tons of red mud were produced annually in the world over the short time range from 2011 to 2018. Red mud represents one of the metallurgical by-products more difficult to dispose of due to the high alkalinity (pH 10–13) and storage techniques issues. Up to now, economically viable commercial processes for the recovery and the reuse of these waste were not available. Due to the high content of iron oxide (30–60% wt.) red mud ranks as a potential raw material for the production of iron through a direct route. In this work, a novel process at the laboratory scale to produce iron sponge (≤ 1300 °C) or cast iron (> 1300 °C) using blast furnace sludge as a reducing agent is presented. Red mud-reducing agent mixes were reduced in a muffle furnace at 1200, 1300, and 1500 °C for 15 min. Pure graphite and blast furnace sludges were used as reducing agents with different equivalent carbon concentrations. The results confirmed the blast furnace sludge as a suitable reducing agent to recover the iron fraction contained in the red mud. For all the conditions tested, the metallization degree was higher than 70%, and the best condition to reduce red mud through blast furnace sludge was identified at 1:1 red mud/blast furnace (B.F.) sludges equal to 0.85 C/Fe2O3.