Characteristics and influencing factors of cadmium biosorption by the stem powder of the invasive plant species Solidago canadensis

To reveal the performance of stem powder of Solidago canadensis as a putatively advantageous biosorbent for removal of Cd(II) from simulated waste water, the kinetic and thermodynamic characteristics of biosorption, the effects of ionic strength, humic acid and the physio-chemical factors on biosorption, as well as the desorption and regeneration processes were investigated comprehensively. The stem of S. canadensis was oven-dried and processed into fine powder then mixed with 5 mg/L, 10 mg/L or 20 mg/L Cd(II) solution. The residual concentration was measured using flame atomic absorption spectrometry. The reacting conditions were optimized to pH = 6.0 with a dosage of 0.5 g/L for contact of 240 min. The results showed that: the biosorption reaction is best described by Langmuir monolayer isotherm and pseudo-second-order kinetic models; thermodynamic analysis indicates an exothermic and entropy-decreasing biosorption process; at the optimal temperature 298 K, the saturated biosorption capacity was 19.34 mg/g, greater than that of rise husk and wheat straw reported literally; the increase of ionic strength was beneficial to the capacity of biosorption, for example 0.01 mmol/L and, 0.1 mmol/L Na+ increased the biosorption capacity from 17.58 mg/g to 19.03 mg/g and 19.50 mg/g; the presence of 20 mg/L Ca (II) Mg(II) or humic acid reduced the biosorption capacity by 62.2%, 44.0% and 51.9%, respectively; growing additional amounts of alkaline earth metal ions or humic acid increasingly reduce the biosorption capacity; using 0.01 mmol/L HCl as an agent to regenerate the Cd(II)-loaded biosorbent, the biosorption efficiency decreased to 69.11% of the first round biosorption after 4 cycles. Our results demonstrate that the stem powder of S. canadensis is a promising biomass-based biosorbent for the removal of Cd(II) from waste water for its fine capacity of biosorption and regeneration.