Influence of mercury retention on mercury adsorption of fly ash

Estimating mercury adsorption capability plays a vital role in verifying whether fly ash could act as a good sorbent for mercury removal. In this work, mercury retention in fly ash is considered to study its effect on mercury adsorption capacity. Six fly ash samples are collected from six different full-scale coal-fired power plants. The mercury adsorption ratio is measured by adsorption tests to characterize mercury adsorption capability of fly ash. The mercury retention in coals and their corresponding fly ashes are also examined. The results show that there is no linear correlation for fly ash between mercury retention ratio and mercury adsorption ratio Such phenomenon results from the fact that mercury retention ratio is determined by mercury adsorption properties of fly ash and mercury concentration of flue gas. The mercury species adsorbed from flue gas occupy the active sites of fly ash, which decrease the adsorption capability of fly ash. However, each as-received fly ash is surrounded with different mercury concentrations of flue gas. Even though two fly ashes have the same active sites for adsorbing mercury, they have different number of occupied active sites for mercury adsorption after flowing along with flue gas. Hence, evaluating the intrinsic mercury adsorption properties of fly ash should pretreat the fly ash samples before adsorption tests by removing out the adsorbed mercury to recover the occupied active sites, with which it may be reasonable to truly manifest the mercury adsorption properties of fly ash.