14
Q. T. Lai et al.
Introduction
Fossil fuels are playing a primary role in the production of heat and electricity globally. Therein, coal has been the largest single source for electric generation. Approximately 38.8% of the global generated electricity has been supplied by coal-derived
power [1]. In 2016, the world consumed 7.50 billion tons of coal, of which 4.92
billion tons of coal was used to produce electricity and heat [2]. Coal ash including
fly ash and bottom ash are the remnants after burning coal at power plants. Coal
ash (CA) was the second-largest anthropological powdery substance after the mine
wastes. Driven by surging electricity needs, the demand for coal keeps increasing.
Consequently, massive coal ash (CA) is produced [3, 4].
Stockpiled CA has been creating numerous problems that are requiring proper
management practices and appropriate recycling technologies. CA is commonly
disposed at open landfills or surface impoundments. Whereas, CA typically includes
toxicities, arsenic, lead, chromium, mercury, cadmium, etc., [5–7] which are known
carcinogens and can damage organs, among other health effects [8]. The improper
management of coal ash or casual lined of the ash ponds enable transmitting the
toxicities to the nearby waterways and soils [9]. Additionally, the massive unused
CA has occupied the vast area of land and cost large sums of money for disposal and
management. Coal ash disposals, especially in the flood zone, also involve inherent
threats to the environment, nearby communities, and human health [10]. The encapsulated uses of CA are concrete and cement production, mining applications, and
structural fills [11, 12].
Hydrometallurgy process has been globally accepted for REE extraction from
coal ash [13]. Acid leaching is a critical method to mobile the low concentration of
REE from the flash ash (FA) sample and acts as a precursor to the following recovery
process [14]. However, there exist numerous investigations on the extraction of REE
from pulverized coal combustion (PC) fly ash but from circulating fluidized bed
combustion (CFBC) fly ash. This study investigates the leaching behavior of critical
rare earths scandium and yttrium from CFBC fly ash in Korea. The dependence
of leaching efficiency on reagent strength, leaching time, and temperature has also
been uncovered. The optimization of leaching conditions provided a higher yield of
scandium and yttrium dissolution.
Materials and Methods
Materials
Chemical and Mineralogical Composition of the FA
The FA sample was collected from a Korean coal-fired power plant coupled with
the circulating fluidized bed combustion (CFBC) boiler. The CFBC FA was dried
Q. T. Lai et al.
Introduction
Fossil fuels are playing a primary role in the production of heat and electricity globally. Therein, coal has been the largest single source for electric generation. Approximately 38.8% of the global generated electricity has been supplied by coal-derived
power [1]. In 2016, the world consumed 7.50 billion tons of coal, of which 4.92
billion tons of coal was used to produce electricity and heat [2]. Coal ash including
fly ash and bottom ash are the remnants after burning coal at power plants. Coal
ash (CA) was the second-largest anthropological powdery substance after the mine
wastes. Driven by surging electricity needs, the demand for coal keeps increasing.
Consequently, massive coal ash (CA) is produced [3, 4].
Stockpiled CA has been creating numerous problems that are requiring proper
management practices and appropriate recycling technologies. CA is commonly
disposed at open landfills or surface impoundments. Whereas, CA typically includes
toxicities, arsenic, lead, chromium, mercury, cadmium, etc., [5–7] which are known
carcinogens and can damage organs, among other health effects [8]. The improper
management of coal ash or casual lined of the ash ponds enable transmitting the
toxicities to the nearby waterways and soils [9]. Additionally, the massive unused
CA has occupied the vast area of land and cost large sums of money for disposal and
management. Coal ash disposals, especially in the flood zone, also involve inherent
threats to the environment, nearby communities, and human health [10]. The encapsulated uses of CA are concrete and cement production, mining applications, and
structural fills [11, 12].
Hydrometallurgy process has been globally accepted for REE extraction from
coal ash [13]. Acid leaching is a critical method to mobile the low concentration of
REE from the flash ash (FA) sample and acts as a precursor to the following recovery
process [14]. However, there exist numerous investigations on the extraction of REE
from pulverized coal combustion (PC) fly ash but from circulating fluidized bed
combustion (CFBC) fly ash. This study investigates the leaching behavior of critical
rare earths scandium and yttrium from CFBC fly ash in Korea. The dependence
of leaching efficiency on reagent strength, leaching time, and temperature has also
been uncovered. The optimization of leaching conditions provided a higher yield of
scandium and yttrium dissolution.
Materials and Methods
Materials
Chemical and Mineralogical Composition of the FA
The FA sample was collected from a Korean coal-fired power plant coupled with
the circulating fluidized bed combustion (CFBC) boiler. The CFBC FA was dried