Part 2 CCT Overview
Environmental Protection Technologies (Technologies to Effectively Use Coal Ash)

5C4. Technology to Recover Valuable Resources from Coal Ash
Technology overview

1. Technology overview
Various R&D activities are being conducted to identify anddesulfurization agent, a rust inhibitor, and as an admixture anddevelop effective coal ash utilization technologies. Potential

filler for polymeric materials (rubber and plastic). Throughtechnical applications that have been studied include thezeolitization, additional potential applications have been

recovery of valuable resources from coal ash through physicalidentified, including utilization as an adsorbent, a catalyst, an ion-and chemical treatments, and the utilization of coal ash as aexchanger, and a desiccant.

2. Valuable resource recovery
Coal ash contains valuable substances including cenosphere(1) Direct hydrofluoric acid extraction method(hollow ash), magnetite silica, alumina, iron oxide, and titanium

An acid extraction method, which uses an acid mixture ofoxide, as well as trace amounts of other valuable metals.

hydrofluoric acid and hydrochloric acid, has been developed to1) Recovery of valuable resources through physical treatment

recover valuable resources from fly ash. The SiO2 recovered isMagnetite recovery through magnetic separation

characteristically of high purity (99.9% or higher) and fine

The recovery of magnetite (Fe3O4) from fly ash is performed priorparticles (1 m or less).

to the chemical treatment process to recover valuable elements(2) Calcination method

such as Si, Al, Ti, and Fe. Magnetite, recovered through aIn the calcination method, calcium is combusted with fly ash tomagnetic separation process, can be used, for example, as anconvert the acid-stable mullite present in the fly ash into acid-alternative to a heavy separation medium.

soluble anorthite or gehlenite, resulting in a high recovery rate of2) Recovery of valuable resources through chemical treatment

AI.

3. Artificial zeolite
Zeolite is a generic term for hydrated crystalline alumina silicate

zeolite production in 1990. In this coal ash zeolite production

that, as one of its characteristics, has a porous structure andprocess, coal ash zeolite is obtained when coal ash is boiled withtherefore a large specific surface area. It also contains ion-sodium hydroxide and stirred. Solid contents are then separated,exchangeable cations and crystallization water that can be

washed and dehydrated. The zeolite produced is of an Na-P type.

adsorbed/desorbed. Because of such characteristics, zeolite canMeanwhile, coal ash zeolite production processes commercialized tobe used, for example, as an adsorbent, a catalyst, or adate are of a batch method, similar to non-coal ash processes,

desiccant1.

while flow-through continuous synthesis processes have also

Treating a coal ash-alkaline aqueous solution mixture2

been developed4. In addition, applications that are expected tohydrothermally produces various kinds of zeolite, depending

use a large volume of zeolite are now being reviewed, with anupon the reaction conditions.

eye on reducing production costs and developing technology to

The Clean Japan Center3 conducted demonstration tests at asynthesize zeolite in ways suitable to each application.

10,000 ton/year-scale demonstration plant built for coal ash

Coal ash
Caustic soda

Boiling/stirring

Buffer tank

Drain waterWashing

NaOH drainage pit

Dehydration

Water drainage pit
Water treatment facilityFig. 1 Coal ash zeolite production process

101

PrimaryproductstorageDryingBagging

Clean Coal Technologies in Japan

4. Utilization in other sectors
1) Desulfurization agent

an alternative to plastic admixtures including calcium carbonate,

Dry desulfurization technology using coal ash has beensilica, alumina, wood flour, and pulp.

commercialized, using a hardened mixture of coal ash, slack3) Otherlime, and gypsum, which have excellent desulfurization

Other than the above, technology development is currently

capabilities.

focused on coal ash characteristics-based applications, such as2) Admixture/filler for polymeric materials (including rubber and plastic)in an agent to prevent rust caused by oxidation in steel-making,Fly ash, since it is a collection of small, round glass-bead-like fine

as well as for use in water purification or for casting sand.

particles, is being studied for possible use as a rubber filler or asStructure

A

Molecular formula

Pore size(A)

Na 12 [(AlO 2 ) 12 (SiO 2 ) 12 ]Na type: 4

27H 2 O

Ca type: 5

Pore volume
CEC(cc/g)(meq/100g)

Na type: 0.3

548

SiO4

PX
AlO4Na 6 [(AlO 2 ) 6 (SiO 2 ) 10 ]Na type: 2.6 Na type: 0.36

15H 2 O514
(The figure is large
but the exchange rateis small.)

Na 86 [(AlO 2 ) 86 (SiO 2 ) 106 ]Na type: 7.4 Na type: 0.24

264H 2 O

473

Cation-containing aluminosilicate found in different forms for different structures/compositions,with each having its own characteristics and applications.

References

1) Environmental Technology Association/The Japan Fly Ash Association: Coal Ash Handbook 2000 Edition, 2000.
2) Akio Itsumi: Japan Soil Science and Plant Nutrition, 58 (3), 1987.
3) The Clean Japan Center: Clean Japan, 86, 1991.
4) Masahiko Matsukata: CCUJ, 12th Annual Conference on Clean Coal Technology lecture collection, 2002.

102