Rice busk biochar treatment to cobalt-polluted fluvo-aquic soil: speciation and enzyme activities.

Rice busk biochar was mixed with cobalt (Co)-polluted soil to examine the efficacy of biochar for Co immobilization and detoxification in fluvo-aquic soil. The Co speciation (modified BCR sequential extraction), fluorescein diacetate (FDA) hydrolysis and soil enzyme activities were investigated. In soil, the Co ions (acid-soluble fraction) could be uptake by biochar due to the microporous structure on the surface, as well as the oxygen-containing functional groups and conjugated structure in the molecular structure. Therefore, when the biochar concentration was lower than the optimum concentration (~6 g·kg-1), there was transformation of Co from the acid-soluble fraction to the oxidizable fraction, resulting in lower environmental risk. However, if the biochar concentration continued increasing, the distribution coefficient of Co in the acid-soluble fraction increased (P < 0.05). The biochar could also reduce the toxicity of Co, resulting in the negative correlations between soil enzyme activities (FDA hydrolysis, urease and alkaline phosphatases) and Co in the acid-soluble fraction (r = -0.816, -0.928 and -0.908, respectively, P < 0.01). When the biochar concentration ranged from 5.83 to 6.76 g·kg-1, the efficacy for Co immobilization and detoxification reached the maxima. To conclude, in fluvo-aquic soil, rice busk biochar is an effective amendment for immobilizing Co ions and reducing the toxicity of Co. The biochar concentration in soil should range from 5.83 to 6.76 g·kg-1 to reach the optimum efficacy.

Maleic, glycolic and acetoacetic acids-leaching for recovery of valuable metals from spent lithium-ion batteries: leaching parameters, thermodynamics and kinetics.

Environmentally friendly acid-leaching processes with three organic acids (maleic, glycolic and acetoacetic) were developed to recover valuable metals from the cathodic material of spent lithium-ion batteries (LiCoO2). The leaching efficiencies of Li and Co by the maleic acid were 99.58% and 98.77%, respectively. The leaching efficiencies of Li and Co by the glycolic acid were 98.54% and 97.83%, while those by the acetoacetic acid were 98.62% and 97.99%, respectively. The optimal acid concentration for the maleic acid-, glycolic acid- and acetoacetic acid-leaching processes were 1, 2 and 1.5 mol l-1, respectively, while their optimal H2O2 concentrations were 1.5, 2 and 1.5 vol%, respectively. The optimal solid/liquid ratio, temperature and reaction time for the leaching process of the three organic acids was the same (10 g l-1, 70°C, 60 min). The thermodynamic formation energy of the leaching products and the Gibbs free energy of the leaching reactions were calculated, and the kinetic study showed that the leaching processes fit well with the shrinking-core model. Based on the comparison in the leaching parameters, the efficacy and availability of the three acids is as follows: maleic acid > acetoacetic acid > glycolic acid.

Cobalt speciation and phytoavailability in fluvo-aquic soil under treatments of spent mushroom substrate from Pleurotus ostreatus.

Cobalt (Co) is a nutrient for soil microorganisms and crops, as well as a worldwide industrial pollutant. When the level of Co exceeds the acceptable limit, this heavy metal can lead to devastating consequences for soil environments. There is considerable attention and concern about elevated levels of Co contaminating soil and crops. Spent mushroom substrate (SMS) is a potential amendment for the adsorption of pollutants, which has potential for resolving Co-polluted soil that spans the world. To investigate the environmental behavior and risks associated with Co in fluvo-aquic soil under specific treatments of SMS from Pleurotus ostreatus, a lab-scale pot experiment was conducted. SMS and exogenous Co were added to soil, which was retained for approximately 30 days. Pakchois (Brassica chinensis L.) were planted in the treated soil for 28 days until harvest. The Co speciation in soil (modified BCR sequential extraction) and Co accumulation in pakchoi tissue were studied. When the SMS concentration was within a range of 0 to 9 g kg-1 (total amount = 0 to 2.7 g), Co in the acid-soluble fraction was transformed to the oxidizable fraction in soil, resulting from the mesh structure on the surface of SMS, as well as the amide and carboxyl in the SMS molecular structure. In this situation, the Co accumulation levels in the pakchois decreased significantly (P < 0.05), indicating the efficacy of SMS for reducing Co phytoavailability. However, when the SMS concentration reached 12 g kg-1, the phytoavailability increased again (P < 0.05). When the SMS concentration ranged from 8.86 to 9.51 g kg-1, the Co phytoavailability in soil reached a minimum, while the biomass of pakchoi reached a maximum. Conclusively, SMS from Pleurotus ostreatus are effective for reducing the Co phytoavailability, as well as for reducing the chance of Co transferring into a human's body through crops (i.e., food consumption). In order to achieve the optimum efficacy, the SMS concentration in soil should be maintained at a range of 8.86 to 9.51 g kg-1.