A new method for simultaneous removal of heavy metals and harmful organics from rape seed meal from metal-contaminated farmland

摘要

Phytoremediation is a promising, cost-effective technique for remediating soil contaminated by heavy metals. When using this approach, however, much contaminated plant material will necessarily be generated that cannot be properly treated after the phytoextraction process. This remains an unsolved problem and thus a major hurdle for the commercial implementation of phytoremediation. This study's main objective was to remove several heavy metals and harmful organics from rape seed meal via hydrochloric with 70% alcohol extraction under different experimentally controlled conditions, namely the extraction concentrations, the reaction time and temperature, and the extraction steps. Our results showed the following: (1) Removal of heavy metals was increased by raising the temperature, or extractant concentrations, or successive extraction steps. The highest extraction efficiency was attained with 1% hydrochloric acid at 25 degrees C for 12 h after three successive extractions; under this condition, the removal of Pb, Zn, Cu, and Cd, respectively, reached 89.1%, 93.9%, 92.3%, and 99.3%. (2) After three successive extractions using 0.5% hydrochloric acid, at 25 degrees C for 12 h, the concentrations of Cd and Pb in rape seed meal were 0.028 and 2.75 mg kg(-1), respectively, which met the current Chinese feed safety standards. Thus, 0.5% hydrochloric acid for the extraction of heavy metals in rape seed meal is economically appropriate. (3) Extraction using hydrochloric acid left little harmful organics rape seed meal, but it little lowered the concentrations of six nutrient elements. The removal of phytic acid, tannins, and glucosinolates, respectively, reached 99.2%, 50.0%, and 85.6%. Importantly, crude protein content as a nutrient was reduced by just 1.4%. In general, hydrochloric extraction is a very thorough cost-benefit method for removing heavy metals from rape seed meal.