Multitudinous components recovery, heavy metals evolution and environmental impact of coal gasification slag: A review.

In recent years, the coal gasification industry has rapidly developed, becoming one of the most promising technologies in the advanced and clean coal chemical industry. As a result, the annual emission of coal gasification fine slag (CGFS) has continuously increased. The present situation of CGFS is regarded as a notorious waste in gasification plants and is rudely landfilled or deposited in slag yards, which leads to a large waste of land resources, the release of dangerous elements, and numerous pollution problems. Although CGFS is classified as industrial solid waste, its unique physical and chemical properties make it a valuable resource that cannot be overlooked. This paper focuses on the resource utilization technology and environmental impact of CGFS. The resource utilization of different components of CGFS has realized the evolution from waste to valuable substances. Moreover, during the disposal and utilization of CGFS, its environmental effects cannot be ignored. The main problems and future research directions are also further proposed. Efforts should be focused on the challenges of the technology, cost, and environmental protection in the application process to achieve industrial application, and ultimately committed to sustainable and green development goals, and promote the sustainable management and conservation of resources.

Efficient dewatering of waste gasification fine slag based on mechanical pressure-vacuum fields: Dewatering characteristics, energy optimization and potential environmental benefits.

Landfill is the major waste disposal method of high-moisture coal gasification fine slag (GFS) which causes the pollution of soil and water and brings the waste of resources. GFS efficient dewatering is an urgent problem to be solved, which is beneficial to realize its resource utilization. In this paper, mechanical pressure and vacuum coupling energy fields are applied to carry out the dewatering processes of GFS. The pressure field provides strong power for water migration, which makes water leave the particle system, while the vacuum field provides traction for water removal from system. The fine slag produced from Coal-to-methanol (named JC) with larger size particles tends to form "bridging" frameworks among particles, which provides water occurrence space and increases the moisture migration resistance. The mechanical dewatering process has an energy advantage interval, when the sample moisture is reduced to a certain degree, the mechanical force field is mainly used for particle friction and breakage but not for moisture migration. Through dewatering process energy optimization, high moisture gasification fine slag can be removed about 15% water within 30s and energy consumption of efficient dewatering is 2.63 kJ/g which is much lower than that of drying. Efficient dewatering is benefit to the GFS recycling which reduces hazardous materials release to environment. The potential effects of high efficiency dewatering process on GFS resource utilization and the possible eco-design framework for products recycled from the waste GFS were proposed. The research results will provide theoretical guidance for the gasification fine slag efficient dewatering and is benefit to the environment.

Multifaceted evaluation of distribution, occurrence, and leaching features of typical heavy metals in different-sized coal gasification fine slag from Ningdong region, China: A case study.

The coal gasification fine slag (CGFS) from the entrained-flow coal gasification unit faces the challenge of safe disposal and clean utilization in the Ningdong region, China. This study aims to provide complete and thorough understanding of the distribution features, chemical speciation, environmental impact, and leaching behavior of typical heavy metals (i.e., V, Cr, Mn, Ni, Cu, Zn, Ba, and Pb) in the CGFS with different size fractions. The results show that the distribution of selected heavy metals in the CGFS has evident particle size dependence. Except for Zn, the other heavy metals in different size fractions mainly exist in chemical speciation of residual form with the ratio of 50.11-86.69 wt%. Moreover, it is found that the heavy metals in the different-sized CGFS show different RAC (risk assessment code) environmental risk levels and TCLP (Toxicity Characteristic Leaching Procedure) leaching concentrations. Especially, Zn in SGFS-C and SGFS-D posed a high-risk level to the environment, while the heavy metal elements of Cr, Mn, Ni, Zn, and Ba in other size fractions are classified as a medium environmental risk. In addition, the TCLP test results indicate that the leaching concentration of Cr, Mn, Ni, Zn, Ba, and Pb exceeds the groundwater-related regulatory limit in China. The pH-dependent leaching experiments suggest that Pb shows the amphoteric behavior, while the leaching mode of other heavy metals seems to be the cationic pattern. Furthermore, the leachability of the selected heavy metals in small-size fractions of the CGFS should be given more consideration at both acid and alkaline pH ranges. The leaching kinetic results demonstrate that the most effective mechanism to describe the leaching process of Cr, Ni, Zn, and Pb in different CGFS size fractions is the diffusion-controlled theory, which is supported by the different morphological traits of spherical mineral particles and carbon particles in the CGFS.

Synthesis of Porous Material from Coal Gasification Fine Slag Residual Carbon and Its Application in Removal of Methylene Blue.

A large amount of coal gasification slag is produced every year in China. However, most of the current disposal is into landfills, which causes serious harm to the environment. In this research, coal gasification fine slag residual carbon porous material (GFSA) was prepared using gasification fine slag foam flotation obtained carbon residue (GFSF) as raw material and an adsorbent to carry out an adsorption test on waste liquid containing methylene blue (MB). The effects of activation parameters (GFSF/KOH ratio mass ratio, activation temperature, and activation time) on the cation exchange capacity (CEC) of GFSA were investigated. The total specific surface area and pore volume of GSFA with the highest CEC were 574.02 m2/g and 0.467 cm3/g, respectively. The degree of pore formation had an important effect on CEC. The maximum adsorption capacity of GFSA on MB was 19.18 mg/g in the MB adsorption test. The effects of pH, adsorption time, amount of adsorbent, and initial MB concentration on adsorption efficiency were studied. Langmuir isotherm and quasi second-order kinetic model have a good fitting effect on the adsorption isotherm and kinetic model of MB.