Using additives in the in-furnace
control of arsenic emissions is
promising for reducing the impact on the downstream selective catalytic
reduction system and blocking the spread of arsenic pollutants into
the environment. The study quantifies the arsenic adsorption capacity
of kaolinite at high temperature and clarifies its fixation pathway
with and without the existence of sodium vapor, which is easily adsorbed
by kaolinite. Experiments about Al-coordination and acid sites of
products, as well as calculations of thermodynamic equilibrium and
the adsorption energy based on density functional theory were performed.
During separated arsenic adsorption, nearly 40% of trivalent arsenic
[As(III)] is oxidized to pentavalent arsenic [As(V)] and bonded to
kaolinite, forming an As–O–Al structure. In this respect,
the arsenic adsorption capacity of kaolinite is 200 μg g–1, with 24% of arsenic shown to be well-crystallized
Al-bound. During the co-adsorption process, 82% of As(III) is oxidized
to As(V) and connected to the Al surface of kaolinite, and the O–Na
groups bond to As around the As–O–Al structure, thereby
forming Na–O–As–O–Al. The arsenic adsorption
capacity increased to 878 μg g–1 with well-crystallized
Al-bound arsenic accounting for 56%. This study demonstrates the potential
for the application of kaolinite as an arsenic adsorbent in the actual
furnace.
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