Biochar as a promising adsorbent to remove heavy metals has attracted much attention globally. One of the potential adsorbents is biochar derived from punica granatum peels, a growing but often wasted resource in tropical countries. However, the immobilization capacity of punica granatum peel biochar is not known. This study investigated the physicochemical properties of punica granatum peel boichars pyrolyzed at 300 °C and 600 °C (referred as BC300 and BC600), and the efficiency and mechanisms of Cu(II) adsorption of five types of material treatments: BC300, BC600, soil only, and soils with biochar amendment BC300 and BC600, respectively, at the rate of 1% of the soil by weight. The results show that BC300 had higher yield, volatile matter content and organic carbon content, and larger pore diameter, but less ash content, surface area, pH, and cation exchange capacity than BC600. The Cu(II) adsorption capacity onto biochars and soils with biochar were greatly influenced by initial ion concentration and contact time. The Cu(II) adsorption capacity of biochar, independent of pyrolysis temperature, was around 52 mg g⁻¹. The adsorption capacity of the soil amended with biochar nearly doubled (29.85 mg g⁻¹) compared to that of the original soil (14.99 mg g⁻¹), indicating superb synergetic adsorption capacity of the biochar-amended soils. The adsorption isotherms showed monolayer adsorption of Cu(II) on biochar, and co-existence of monolayer and multilayer adsorption in soils with or without biochar amendment. Results also suggest that the adsorption process is spontaneous and endothermic, and the rate-limiting phase of the sorption process is primarily chemical. This study demonstrates punica granatum peel biochar has a great potential as an adsorbent for Cu(II) removal in soil.

The distribution of forest biomass in a river basin usually has obvious spatial heterogeneity in relation to the locations of the upper and lower reaches of the basin. In the subtropical region of China, a large amount of forest biomass, comprising diverse forest types, plays an important role in maintaining the balance of the regional carbon cycle. However, accurately estimating forest ecosystem aboveground biomass density (AGB) and mapping its spatial variability at a scale of river basin remains a great challenge. In this study, we attempted to map the current AGB in the Xiangjiang River Basin in central southern China. Three approaches, including a multivariate linear regression (MLR) model, a logistic regression (LR) model, and an improved k-nearest neighbors (kNN) algorithm, were compared to generate accurate estimates and their spatial distribution of forest ecosystem AGB in the basin. Forest inventory data from 782 field plots across the basin and remote sensing images from Landsat 5 in the same period were combined. A stepwise regression method was utilized to select significant spectral variables and a leave-one-out cross-validation (LOOCV) technique was employed to compare their predictions and assess the methods. Results demonstrated the high spatial heterogeneity in the distribution of AGB across the basin. Moreover, the improved kNN algorithm with 10 nearest neighbors showed stronger ability of spatial interpolation than other two models, and provided greater potential of accurately generating population and spatially explicit predictions of forest ecosystem AGB in the complicated basin.

The planting of trees on mine wastelands is an effective, long-term technique for phytoremediation of heavy metal-contaminated wastes. In this study, a pot experiment with seedlings of Koelreuteria paniculata under six treatments of local mine wastes was designed to determine the major constraints on tree establishment and to evaluate the feasibility of planting K. paniculata on manganese mine wastelands. Results showed that K. paniculata grew well in mine tailings, and also under a regime of equal amounts of mine tailings and soil provided in adjacent halves of pots. In contrast, mine sludge did not favor survival and growth because its clay texture limited fine root development. The bio-concentration factor and the translocation factor were mostly less than 1, indicating a low phytoextraction potential for K. paniculata. K. paniculata is suited to restore manganese mine sludge by mixing the mine sludge with local mine tailings or soil.