Enrichment of Residual Carbon in Coal Gasification Fine Slag via Wet Sieving Separation with Ultrasonic Pretreatment.

To overcome the environmental and economic challenges posed by the increasing amounts of the coal gasification slag, here, a simple and efficient method for enriching the residual carbon from the coal gasification fine slag was proposed. The residual carbon enrichment pattern in the particle size distribution of coal gasification fine slags after the ultrasonic pretreatment was mainly enriched toward the 500-250 µm and 250-125 µm particle size classes by analyzing the changes in the particle size distribution and apparent morphology. The pulp pretreatment at the ultrasonic output power of 270 W for 4 min was determined as the optimal experimental condition with respect to the yield, ash content, and ash rejection of the concentrates. Compared to the conventional wet sieving separation, the yield and ash content of the final concentrates were reduced by 7.99 and 14.96%, respectively. Moreover, the ash rejection of the final concentrates was as high as 88.51%, indicating an increment of 11.63% than the conventional wet sieving separation. Furthermore, thermogravimetric analysis confirmed that the final concentrates exhibited the lowest reactivity; however, these demonstrated had the highest carbon content (nearly 70%) with 27.27% ash content. The combustion characteristics analysis showed that the wet screening concentrate after ultrasonic pretreatment had the highest composite combustion characteristic index (S) of 3.17 × 10-8, as compared to the raw and conventional sieving concentrates.

Application of Roasting Flotation Technology to Enrich Valuable Metals from Spent LiFePO4 Batteries.

The application of lithium-ion batteries (LIBs) in electric vehicles has attracted wide attention in recent years, especially LiFePO4 batteries that have been extensively used in large electric buses and cars. The increased demand for LIBs has greatly stimulated lithium-ion battery production, which subsequently has led to greatly increased quantities of spent LIBs. From the perspective of environmental protection and resource recovery, the recycling of spent LIBs is of great significance. In this study, the roasting flotation technology was applied to enrich valuable metals from the mixed electrode powder of spent LiFePO4 batteries. Roasting could thoroughly remove the organic outer layer coated on the surface of electrode-active materials, which improved the flotation enrichment efficiency of valuable metals in the mixed electrode powder of spent LiFePO4 batteries. Under the optimum conditions of roasting at 500 °C for 1 h, the enrichment efficiency of Li and Fe reached the best. The recovery and the enrichment ratio of Li were 95.87% and 1.37, respectively, while the recovery and the enrichment ratio of Fe were 95.25% and 1.36, respectively. Roasting flotation was an efficient process to enrich valuable metals from spent LiFePO4 batteries without wasting graphite resources.

Adsorption of ammonia nitrogen and phenol onto the lignite surface: An experimental and molecular dynamics simulation study.

Ammonia nitrogen and phenol are typical inorganic and organic pollutants in the coal chemical wastewater, respectively. In this study, the adsorption characteristics of ammonia nitrogen and phenol on lignite were investigated through experimental and molecular dynamics simulations. The results show that the adsorption of ammonia nitrogen was carried out via ion exchange, which was significantly faster than the adsorption of phenol driven by the π-π interaction. In the binary adsorption, the surface electronegativity of lignite decreased with the adsorption of ammonia nitrogen thereby promoting the adsorption of phenol. However, the extent of ammonia nitrogen adsorption was slightly reduced in the presence of phenol. Molecular dynamics simulation results indicated that the adsorption of phenol molecules on the lignite surface was closer than that of ammonium ion. The addition of ammonium ions could enhance the adsorption of phenol molecules on the lignite surface. The simulation results were well consistent with the experimental findings. This study indicates lignite has a promising potential in coal chemical wastewater adsorption pretreatment.

Effect of ultrasonic standing waves on flotation bubbles.

Ultrasonic flotation was an effective method to float fine coal. In this study, the effects of the standing waves with different frequencies on ultrasonic flotation were investigated. The dynamic processes of bubble and coal-bubble were revealed by a high-speed camera. The results showed that under the action of Bjerknes force, bubble aggregates were formed within 450 ms and coal bubble aggregates were formed within 20 ms. The bubble aggregates were statistically analyzed by image processing method. The number of aggregates and small bubbles in the ultrasonic field at 100 kHz was greater than those at 80 and 120 kHz. Besides, 100 kHz ultrasonic flotation achieved the highest yields of clean coal (35.89%) and combustible recovery (45.77%). The cavitation bubbles acted as either a "medium" or an "inclusion", entrapping and entraining the coal particles in the flotation pulp. It promoted the aggregation of bubbles with coal particles, so the flotation efficiency was effectively improved in the presence of ultrasonic standing waves.