An investigation on the modelling of kinetics of thermal decomposition of hazardous mercury wastes

Abstract

h i g h l i g h t s• A reaction mechanism of thermal treatment of hazardous mercury waste is postulated.• The kinetic model for the thermal decomposition of mercury solid waste is deduced.• A methodology to investigate reaction order models in solid systems is proposed.• The thermal decomposition of mercury waste is described by two modelling approaches. a r t i c l e i n f o t r a c tThe kinetics of mercury removal from solid wastes generated by chlor-alkali plants were studied. The reaction order and model-free method with an isoconversional approach were used to estimate the kinetic parameters and reaction mechanism that apply to the thermal decomposition of hazardous mercury wastes. As a first approach to the understanding of thermal decomposition for this type of systems (poly-disperse and multi-component), a novel scheme of six reactions was proposed to represent the behaviour of mercury compounds in the solid matrix during the treatment. An integration-optimization algorithm was used in the screening of nine mechanistic models to develop kinetic expressions that best describe the process. The kinetic parameters were calculated by fitting each of these models to the experimental data. It was demonstrated that the D 1 -diffusion mechanism appeared to govern the process at 250• C and high residence times, whereas at 450 • C a combination of the diffusion mechanism (D 1 ) and the third order reaction mechanism (F 3 ) fitted the kinetics of the conversions. The developed models can be applied in engineering calculations to dimension the installations and determine the optimal conditions to treat a mercury containing sludge.

Preparation of activated carbon from spent catalyst with mercury by microwave‐induced CO2 activation

“…Depending on the alkalinity of the tested sample, different buffers may be used. Based on the provisions of the U.S. Department of Energy, the concentration of mercury in the permeate is lower than 0.2 mg/L, and acetate/acetate buffer at pH 4.93 is used …”

Desorption kinetic study of mercury species in spent mercury chloride catalyst from polyvinyl chloride production process

“…For non-isothermal reaction rate expression, Equation (6), can be obtained by introducing the heating rate, β = dT/dt, in Equation (5).…”

“…In order to eliminate or reduce the harm of spent mercury catalysts, some efforts have been made with regard to develop new processing methods . The type of alkali, concentration of alkali, reaction temperature and time were studied by Xiaoyan Wang et al .…”

“…The type of alkali, concentration of alkali, reaction temperature and time were studied by Xiaoyan Wang et al . using chemical process, Minghui Chen et al . developed a special multicomponent catalyst with activated carbon and the results indicated that the Cd 2+ , Hg 2+ , and Cl − could not only increase the activity of catalyst, but also decrease the loss of mercury.…”

“…In order to eliminate or reduce the harm of spent mercury catalysts, some efforts have been made with regard to develop new processing methods [5][6][7][8][9][10][11]. The type of alkali, concentration of alkali, reaction temperature and time were studied by Xiaoyan Wang et al [5] using chemical process, Minghui Chen et al [6] developed a special multicomponent catalyst with activated carbon and the results indicated that the Cd 2+ , Hg 2+ , and Cl − could not only increase the activity of catalyst, but also decrease the loss of mercury. Yaxiong Zhang [7,8] studied the recovery of mercury by the chlorine oxidation and high efficiency was realized, while, unbalanced research between process parameters determination researches and mechanism researches of mercury removal process in the spent catalysts is not conducive to solve this problem.…”