Removal of Gas-Phase As₂O₃ by Metal Oxide Adsorbents: Effects of Experimental Conditions and Evaluation of Adsorption Mechanism

Abstract

This research studies the adsorption of gas-phase As 2 O 3 by CaO, Fe 2 O 3 and Al 2 O 3 , using a fixed-bed reactor with an arsenic continuous generation device. The adsorption of gas-phase arsenic on CaO and Fe 2 O 3 is mainly chemical adsorption at 600−900 °C. The adsorption quantity and efficiency decreases as the temperature increases. Iron(III) oxide has the best arsenic adsorption ability, followed by calcium oxide and then aluminum oxide. The incoming arsenic concentration was varied, from 4.5 × 10 −6 v/v to 13.5 × 10 −6 v/v, to determine if this had any effect on adsorption, which revealed that the adsorbent did not become saturated under the experimental conditions used. The adsorption efficiency for each adsorbent was affected by the adsorption temperature, and the same adsorption efficiency was achieved regardless of the inlet arsenic concentration. Intrinsic reaction kinetics of CaO and Fe 2 O 3 with arsenic oxide was studied. The activation energies of CaO and Fe 2 O 3 are 12.17 kJ/mol and 25.99 kJ/mol, respectively. The reaction orders of Fe 2 O 3 and CaO are ∼1.1 and 0.8, respectively.

Review of arsenic behavior during coal combustion: Volatilization, transformation, emission and removal technologies

“…Kinetic parameters could be signficantly different because different kinetic equations were adopted and different experimental parameters were applied. However, the reaction order with respect to arsenic concentration is close to 1, which appears to be a common conclusion [69,71,75,80,237].…”

“…In the recent work of Zhang et al [75], the conclusions of Chen et al [81] were partially validated. Furthermore, through thermodynamic simulation, Zhang et al [75] found that the adsorption process (described as Eq.2) was an exothermic reaction which could explain the temperature impact on arsenic.…”

“…Compared with the low-temperature range, the adsorption product Ca3(AsO4)2 in the high-temperature range was less thermally stable, and the decomposition of Ca3(AsO4)2 at 500-1050ºC led to the reduced adsorption capacity of CaO. In the recent work of Zhang et al [75], the conclusions of Chen et al [81] were partially validated. Furthermore, through thermodynamic simulation, Zhang et al [75] found that the adsorption process (described as Eq.2) was an exothermic reaction which could explain the temperature impact on arsenic.…”

“…A strong positive relationship was found between arsenic and iron. In addition, Zhang et al [75] conducted As2O3(g) adsorption experiments with different metal oxides. The results showed that the arsenic adsorption efficiency of Fe2O3 was around 57% and was significantly higher than for other metal oxides, also revealing that Fe2O3 and As2O3 reacted to form stable arsenates.…”

Inhibitory effects of CaO/Fe2O3 on arsenic emission during sewage sludge pyrolysis

“…Shen et al (2015) maintained that CaO could react with arsenic compounds to form Ca (AsO 2 ) 2 above 1273 K by calculation. Zhang et al (2015) believed that As 2 O 3 steam could be absorbed by ferric oxide (Fe 2 O 3 ) and transformed to iron arsenate (FeAsO 4 ). However, most of these experiments were only conducted to investigate the interactions between As 2 O 3 and CaO/Fe 2 O 3 , and some of above interactions were put forward in oxygen atmosphere.…”