Thermochemical conversion characteristics and kinetics of Cu- and Mn-contaminated biomass using a continuous pyrolysis-combustion method

Phytoremediation technology has been well developed in the remediation of heavy metal pollution due to its low cost, in-situ disposal, permanent treatment, and environmental friendliness. The harvested phytoremediation plants are the combustible solid wastes and the disposal of them has drawn much attention. To realize clean disposal and utilization of Cu- and Mn-polluted plants, a two-stage thermochemical conversion technology combining pyrolysis and combustion was developed. In the continuous heating process, the pyrolysis characteristics at different final temperatures and combustion products of pyrolysis residual were analyzed in TG-MS and fixed bed reactor. Using the Coats-Redfern method, different kinetic models were tried to fit the pyrolysis process. It is demonstrated that these models can not be used to fit the whole pyrolysis and the kinetic parameters showed obvious segmentation characteristics. Apparent activation energies in the second and third stages during pyrolysis are 39.73–42.04 kJ/mol and 2.20–4.78 kJ/mol respectively. Additionally, experimental results exhibited that the weight loss rate increases from 62.5% to 66.2% when the pyrolysis temperature increases from 450 °C to 600 °C. Meanwhile, the retention ratio of Cu decreases from 64.6% to 26.4% while the ratio of Mn decreases from 58.8% to 34.4%.