Pyrolysis temperature significantly affects the properties of biochar, which in turn can affect the removal of heavy metal ions and the underlying mechanism. In this work, biochars from the pyrolysis of maize straw at 300, 400, and 500 °C (BC300, BC400, and BC500, respectively) and wheat straw at 400 °C (WBC400) were investigated. The influence of production temperature on the adsorption of Hg²⁺, Cd²⁺, and Pb²⁺ by maize straw biochar was investigated by the characterization of the biochars and by adsorption tests. The adsorption capacities of maize and wheat straw biochar were compared in an adsorption experiment. Biochar BC400 showed the best physical and chemical properties and had the largest number of surface functional groups. The pseudo-second-order kinetic model was more suitable for describing the adsorption behavior of metal ions to biochar. The Langmuir model better fit the experimental data. Biochar BC400 had a higher adsorption speed and a stronger adsorption capacity than WBC400. The sorption of Pb²⁺ and Hg²⁺ to maize straw biochar followed the mechanisms of surface precipitation of carbonates and phosphates and complexation with oxygenated functional groups and delocalized π electrons. The adsorption mechanism for Cd²⁺ was similar to those of Hg²⁺ and Pb²⁺, but precipitation mainly occurred through the formation of phosphate. In the multi-heavy-metal system, the adsorption of Cd²⁺ by BC400 was inhibited by Pb²⁺ and Hg²⁺. In summary, BC400 biochar was most suitable for the adsorption effect of heavy metals in aqueous solution.

The existence of macropores acutely enhances the capacity of soil to conduct water, gas, and chemicals. The capacity of macropores to transport water extremely depends on their spatial characteristics. However, the effect of the horizontal spatial distribution of macropores (especially the position characteristics of macropores) on water infiltration is still ambiguous. Therefore, this study utilizes the approach of numerical simulation to investigate the general pattern of the effects of horizontal spatial distribution characteristics of macropores (such as number, pore size and position) on water infiltration. Given the limitations on the ability to characterize the macropore position from the existing spatial characteristic parameters of macropores, two new statistical parameters (spatial dispersion, $\gamma$, and spatial deviation, ${\gamma }^{*}$) are established to characterize the position relationships among macropores and between the macropores and the observation area, respectively. The results show that the larger the macropore number and the more uniformly macropores are distributed, the greater the soil permeability and the preferential flow degree, while the pore size hardly affects the water transport. Additionally, comparison between number and position effects reveals that the macropore number is the dominant factor when the macropore number is relatively small, but this relationship will reverse when the macropore number is relatively large. This study provides a novel meals to investigate the effect of macropore position on water infiltration, and emphasizes that besides the macroporosity, number and position are also significant for quantifying soil permeability.

The conventional advection-dispersion equation (ADE) has been widely used to describe the solute transport in porous media. However, it cannot interpret the phenomena of the early arrival and long tailing in breakthrough curves (BTCs). In this study, we aim to experimentally investigate the behaviors of the solute transport in both homogeneous and heterogeneous porous media. The linear-asymptotic model (LAF solution) with scale-dependent dispersivity was used to fit the BTCs, which was compared with the results of the ADE model and the conventional truncated power-law (TPL) model. Results indicate that (1) the LAF model with linear scale-dependent dispersivity could better capture the evolution of BTCs than the ADE model; (2) dispersivity initially increases linearly with the travel distance and is stable at some limited value over a large distance, and a threshold value of the travel distance is provided to reflect the constant dispersivity; and (3) compared with the TPL model, both the LAF and ADE models can capture the behavior of solute transport as a whole. For fitting the early arrival, the LAF model is less than the TPL; however, the LAF model is more concise in mathematics and its application will be studied in the future.

In this study, biochar and KH 2 PO 4 were used as remediation agents, and they were added separately or in combination to explore the remediation effects and mechanisms of the combined application of biochar and KH 2 PO 4 on the artificially prepared soil at heavy metal compound contaminated site, investigate the effects of the addition of remediation agents on the chemical forms of heavy metals, and study the interaction rules between different heavy metals. The indoor culture and restoration method was use to artificially prepare Hg, Cd and Pb compound contaminated soil from mine acidic soil, and that physicochemical property and heavy metal forms of the soil were detected after culture for 10, 25, 40 and 55d, to compare the restoration effects of two kinds of passivators, namely corn straw biochar and KH 2 PO 4 , applied alone and in combination on the Hg, Cd and Pb compound contaminated soil. The main results showed that except the pH value of the KH 2 PO 4 treatment group remained unchanged, the pH value, EC and available phosphorus content of the soil after different treatments were increased. The effect of applying biochar and KH2PO4 alone is not good. The combined application of biochar and KH 2 PO 4 had the best curing effect on Pb and promoted the transformation of Pb from the exchangeable state and organic state to the carbonate-bound state, the iron-manganese oxide-bound state and the residue state. The field verification of soil remediation effect showed that with the prolongation of culture time, the proportion of stable state of soil heavy metal ions was increased and the exchangeable state was decreased. Biochar and KH 2 PO 4 had good passivation effect on heavy metals Hg, Cd and Pb in outdoor compound polluted soil.

To understand the cause of the high content of phosphorus in the North Chaohu Lake Catchment of China, the distribution of the total phosphorus in groundwater and the dissolution of rock phosphorus near Chaohu Lake were investigated, and a few interesting findings have been revealed. Firstly, four main processes affecting the groundwater quality in North Chaohu Lake Catchment were identified with the results of factor analysis, including anthropogenic activities and the dissolution of carbonate rocks, phosphorus, and fluorine-bearing minerals. Secondly, the dissolution of rock phosphorus can be well described using the one-dimensional diffusion equation, with a semi-infinite boundary condition, and the Langmuir kinetic equation. A relatively low ambient temperature (less than 25 °C) was probably responsible for the small diffusion coefficient compared to that of the previous studies. Thirdly, the high-potential maximum dissolution of rock phosphorus (C_max) indicated that the dissolution of rock phosphorus could pose a risk to the ambient water body, and C_max was found to be independent of the total rock phosphorus content.