Abstract:【Objective】Cadmium (Cd) is a harmful element to the human body and can cause many serious diseases. At present, many soils are faced with serious Cd contamination. For example, the soil in Yunnan Province highly polluted by Cd, and necessary steps need to be taken to remedy this situation. The application of biochar to soils is a common way to remedy soil Cd contamination, therefore, this research is designed to study the properties of biochar from different plant sources and evaluate their application effect on Cd pollution in the Dongchuan area, Yunnan Province. 【Method】The isothermal adsorption-desorption and adsorption kinetic characteristics of rice straw biochar (RBC), wheat straw biochar (WBC), corn straw biochar (MBC), hemp straw biochar (HBC), sesbania biochar (TBC) and peanut shell biochar (PBC) were studied; Through pot experiments, the effects of the above biochar on Cd fraction in Cd-contaminated soil and Cd uptake by Lactuca sativa L. in Dongchuan were analyzed. 【Result】Fitting results of adsorption models showed that Langmuir adsorption isotherm and the pseudo-second-order model could better simulate the adsorption process of Cd by biochar. TBC’s maximum saturated adsorption capacity was the highest, 37.1 mg·g-1 in the isothermal adsorption model and 27.9 mg·g-1 in the adsorption kinetic model, respectively. The desorption rates of WBC, RBC and TBC were lower than those of MBC, HBC and PBC, and no more than 10% under each concentration gradient. Fourier transform infrared spectroscopy (FTIR) analysis showed that TBC contained more oxygen-containing functional groups (OH-, C=O etc.). Also, the XRD analysis showed the biochars were mainly composed of C and Si elements, while different biochars also had some different elements (e.g. Fe, Mn etc.). Compared with the treatment without biochar (CK), WBC, MBC, HBC, TBC and PBC treatments significantly reduced the content of soil available Cd. Among them, the maximum decrease was observed for TBC (24.32%). At the same time, the Cd fraction changed from an acid soluble state to a reducible state, oxidizable state and residual state. Compared with the treatment without biochar, WBC, MBC, HBC and TBC treatments significantly reduced the Cd content in the aboveground parts of Lactuca sativa L. (P<0.05), and the maximum decrease occurred in HBC (26.40%). In addition, WBC and HBC treatments significantly reduced the translocation factors of Cd in Lactuca sativa L., which were 0.662 0 and 0.692 8 respectively. The results of ABT (aggregated promoted tree) analysis showed that soil soluble organic carbon (DOC) and soil pH were the main influencing factors of soil available Cd, with a significant negative correlation, and the contribution rates were 33.0% and 21.9% respectively. 【Conclusion】In conclusion, all the biochars from different plant sources can reduce the availability of Cd in Cd-contaminated soil in Dongchuan, change the Cd fraction in soil, and reduce the absorption and transport of Cd by plants. There are differences between different biochars. Moreover, TBC can be selected to remedy Cd-contaminated soil in the Dongchuan area through the results of the isothermal adsorption test, adsorption kinetics test and pot experiments.

Abstract:【Objective】The influence of free iron oxide on the adsorption and desorption of Se(Ⅳ) in a lateritic red soil and red soil in the selenium-rich area of Guangxi was studied. 【Method】The adsorption and desorption characteristics of Se(Ⅳ) in the soil before and after removing free iron oxide were compared by isothermal adsorption and desorption experiments. Zeta potential, scanning electron microscopy and energy spectrum analysis and Fourier transform infrared spectroscopy was used to explore the influencing mechanism.【Result】The results showed that the adsorption process for Se(Ⅳ) fitted the Langmuir and Freundlich models, with correlation coefficients ranging between 0.920~0.995. After removing free iron oxide of red soil and lateritic red soil, the zeta potential became more negative and changed from -24.42 and -18.06 mV to -33.06 and-26.43 mV. Also, the specific surface area was decreased. This observation correlated with the lower adsorption capacities of the soils after the removal of free iron oxide. Hence, the order of maximum adsorption capacity was: lateritic red soil (1 399 mg·kg-1) > red soil (1 336 mg·kg-1) > DCB-treated lateritic red soil (444 mg·kg-1) > DCB-treated red soil (352 mg·kg-1). The desorption rates of the tested soils were between 2% and 7%, while that of DCB-treated soils were higher than that of the original soils. The FTIR peak fitting analysis showed that the soils reacted with selenium mainly through the oxygen-containing groups such as -OH, Fe-O and C=O. After the removal of iron oxide, the effect of Fe-O in the adsorption was weakened or disappeared.【Conclusion】Free iron oxide can significantly increase the adsorption capacity and strength of soil for Se(Ⅳ) and reduce the release of Se(Ⅳ) by its physical and chemical properties and surface groups.

Abstract:【Objective】 Some changes in the external environment are often observed after the remediation of heavy metal polluted soils with solidification stabilization technology. Thus, an important scientific question worth discussing is whether the inactivated heavy metals will be released again and migrate in the soil, causing pollution risk, and under what conditions.【Method】 In order to reveal the effects of different chemical factors on the activation and migration of heavy metals in contaminated soil, the desorption and migration behavior of Cu2+ and Cd2+ in soil under different ionic strength, pH and cation types (Ca2+, Na+) were studied by laboratory soil column experiments. 【Result】 In general, the peak leaching concentration of Cu2+ and Cd2+ increased with the increase in ionic strength. Using CaCl2 as a leaching agent, the desorption capacity of Cu2+ and Cd2+ increased at 0.005, 0.01, 0.05 and 0.1 mol·L–1 CaCl2, and the desorption capacity of Cd2+ was higher than that of Cu2+. However, 0.5 mol·L–1 CaCl2 inhibited the desorption of Cd2+ and the desorption of Cu2+ was higher than that of Cd2+. When pH decreased, the desorption of Cu2+ and Cd2+ increased, that is, the acidic environment was conducive for the desorption of Cu2+ and Cd2+. However, the concentration peak of Cu2+ and Cd2+ at pH 3 was smaller than that at pH 4 and 5. Ca2+ was more favorable for the desorption of Cu2+ and Cd2+ than Na+, but NaCl solution was more favorable for the desorption of Cu2+ at 0.005 mol·L–1. Also, the concentration of Cu2+ in the leaching stage with deionized water was higher than that in the leaching stage with CaCl2. In addition, soil particles exhaled at 0.005, 0.05 and 0.5 mol·L–1 NaCl, and the flow rate decreased at 0.05 and 0.5 mol·L–1 NaCl.【Conclusion】 The increase in ionic strength, decrease in pH and presence of divalent cations were beneficial to the desorption and migration of heavy metals in soil. This study provides a theoretical basis for soil remediation and heavy metal release after soil remediation.

Abstract:【Objective】This study aimed to analyze the change of phosphorus fixation capacity and release potential in different occurrence layers of red paddy soil, to clarify the release mechanism of fixed phosphorus (P), and to evaluate the loss risk of P in red paddy soil with different planting years.【Method】Soil samples were collected from the bottom to the top of three typical red paddy fields in Yingtan, Jiangxi Province. These paddies included a mid-phase paddy field (MP), a new paddy field (NP) and an old paddy field (OP). Based on the adsorption-desorption experiment and structural equation model, the variation differences and influencing factors of phosphorus retention capacity (PSI), maximum capacity of soil fixed phosphorus (MCSP) and the release potential of the soil were analyzed.【Result】With the increase of pedogenic horizons depth, PSI and MCSP of red paddy soil gradually increased, and the order of their changes were: MP > NP > OP and NP > MP > OP. The desorption capacity of electrostatically adsorbed state P (CaCl2-P) of OP, MP and NP profiles and the desorption capacity of specific adsorbed state P (EDTA-P) in the OP profile gradually decreased with the increasing profile depth. Also, the EDTA-P in MP (except Ap1 layer) and NP profiles and residual P (Red-P) in soil pedogenic horizons followed an opposite trend. With the increase of profile depth, the CaCl2-P/EDTA-P in the pedogenic horizons of the OP profile increased, which was significantly higher than that in the MP and NP profiles. The adsorption-desorption capacity of phosphorus in red paddy soil is mainly affected by SOM (soil organic matter), TP (total phosphorus), pH and iron-aluminum oxides. The interaction between SOM, TP, pH and iron-aluminum oxides jointly regulates the number of phosphorus adsorption sites and the strength of adsorption-desorption capacity in red paddy soil.【Conclusion】In this research, it was found that the Ap layer of red paddy soils was characterized by the weak capacity of the soil P sorption and strong capacity of P desorption and a high risk of soil P loss. Meanwhile, Br and C layers showed a stronger soil P sorption capacity and a weaker P desorption capacity, and a higher soil P fixation capacity than the Ap layer. Compared with the profile of OP, the exogenous P adsorbed in pedogenic horizons of NP and MP was more easily converted to the specialized adsorption state and residual state P, thus, resulting in a reduced risk of soil P loss. The risk of P loss in the OP profile was relatively higher than its counterparts, and timely regulatory measures are needed.

Abstract:[Objective] Desorption of antibiotics in soils in the presence of microplastics is key to its migration, transformation, and bioavailability. The objective of this study was to reveal the desorption characteristics of sulfamethoxazole in an artificial antibiotic contaminated soil in the presence of five different microplastics.[Method] Batch equilibrium desorption experiments were carried out using an acid paddy soil that was spiked with 33.4 mg·kg–1 sulfamethoxazole and was aged for 5 days before use. Five polymeric microplastics including polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET) (1.67% and 3.33%). The microplastics were added to the soil individually and a soil:solution ratio of 1:10 was maintained in the experiment. The supernate was sampled for the sulfamethoxazole analysis using high-performance liquid chromatography (HPLC) from 0.25 to 96 h during the desorption kinetic experiment. Also, different concentration of NaCl and fulvic acid were added into the soil-microplastics mixture system to study the effect of salinity and dissolved organic matter (DOC) on sulfamethoxazole desorption, respectively.[Result] The results indicated that the desorption rate of sulfamethoxazole declined significantly and a slow desorption phase was observed from 10 h to 48 h after the addition of polyethylene and polystyrene microplastics. The equilibrium desorbed concentration of sulfamethoxazole declined significantly (P < 0.05) in the presence of polyethylene and polyvinyl chloride microplastics. The influence of sodium and calcium ions on sulfamethoxazole desorption from the soil was not affected by the addition of microplastics. However, the influence of fulvic acid on sulfamethoxazole desorption was mitigated after the addition of microplastics in general. Importantly, with an elevated concentration of fulvic acid, the decline of sulfamethoxazole desorption was negligible.[Conclusion] Generally, the desorption of sulfamethoxazole from soils was altered in the presence of microplastics. In soils with a relatively high concentration of DOC, elevated sulfamethoxazole desorption was observed. Therefore, this study highlights the migration and bioavailability of sulfamethoxazole in soils contaminated with microplastics and how different solvents influenced its desorption.

Abstract:Chemical warfare agents containing organoarsenic compounds such as Clark I (diphenylcyanoarsine) and Clark II (diphenylchloroarsine) were widely produced and used during World Wars I and II. After the wars, remains of these agents were simply dumped into the sea or buried underground, thus inevitably polluting the soil-water environments of the sits where they were disposed with the arsenic contained in the chemical weapons. In the environment, these abandoned chemical agents are easily hydrolyzed and oxidized into diphenylarsinic acid (DPAA), rather stable in structure, and other organoarsenic compounds. So far, DPAA has been detected in quite a number of the areas where these chemical weapons were dumped. The detection has aroused extensive concerns because the presence of DPAA may bring about environmental and health risks. Scholars both at home and abroad have already begun doing some researches, trying to find ways to analyze DPAA in the soil and water environments, determine their status and behaviors and remedy the polluted environments. However, few have done any to summarize systematically progresses in the research. In this paper, a review is presented to introduce some high-effect inorganic and organic extractants and GC as well as LC analytical methods for DPAA in the soil, and sources and status of the pollutant in the soil-water environments. Generally speaking, the DPAA contaminated areas are located mainly in Northeast China, and South and Southeast Japan. Especially in the chemical weapons dumping sites, the concentration of total arsenic is far beyond the criteria for safety. At the same time, the paper also discusses how DPAA is adsorbed/desorbed, translocated and transformed in the soil-water environment, what are the factors affecting the processes and what are the mechanisms. Studies in the past reported that the adsorption/desorption of DPAA in soil was controlled by a variety of factors, including pH, inorganic ions, Fe/Al oxides, organic matter, redox potential (Eh), etc. and adsorption of the substance was completed via ligand exchange reactions between hydroxyl groups of Fe/Al oxides and arsenate of DPAA, rather than the hydrophilic effect of organic matter; the effective transformation of DPAA in the soil occurred under flooded anaerobic conditions, and under sulfate-reducing conditions, in particular; and iron reduction and sulfate reduction were the two key factors controlling desorption and transformation of DPAA. In the end, the paper elaborates the physical, chemical and biological technologies available for remediation of DPAA contaminated soil-water environments, and their remediation efficiency, controlling factors and mechanisms as well. In terms of physic-chemical remediation, application of activated carbon, Fenton and Fenton-like oxidation and photochemical degradation has been demonstrated to be able to effectively remove DPAA in soil-water environments. In terms of bioremediation, certain progresses have been made, like screening of highly efficient DPAA degrading bacteria, unfolding microbial remediation and combined microbial-phytoremediation and previewing directions of the future researches. The paper holds that all the relevant research findings will serve as theoretical reference for future in-depth studies on DPAA pollution of soil-water environments, remediation of DPAA polluted environments, and protection of environmental quality and human health from DPAA pollution. For further researches, emphases should be laid on the following aspects: (1) To perfect quality assurance and quality control system for DPAA analytical methods, with focus on development of standard alternatives, purgation of internal standards and markers; (2) To launch investigations on scope and extent of DPAA contamination, while taking into the consideration of geographical locations, soil types and land-use patterns of the chemical weapon burial sites; (3) To explore forms of DPAA bonding with soil colloids, clay minerals and oxides in the soil and molecular binding mechanisms, and elucidate the mechanisms responsible for adsorption/desorption, translocation and transformation of DPAA in multi-media environment and at microscopic interfaces; (4) To explore for develop new remediation materials, intensify researches on physic-chemical-phyto combined remediation and continue to screen out highly efficient DPAA degrading bacteria and probe mechanisms of their effectiveness at molecular as well as genetic levels, while integrating genetic engineering, molecular biology with phytoremediation technologies, so as to eventually establish a bioremediation technical system applicable to DPAA contaminated media different in type and condition.

Abstract:【Objective】To investigate in depth effects of ionic strength on desorption of Cu(II) pre-adsorbed on surface of variable charges, two variable charge soils, Ali-Haplic Acrisol and Hyper-Rhodic Ferrasol were employed in a successive desorption experiment, in which the soils had been pre-treated with copper ions in de-ionized water or 0.1 mol•L-1 NaNO3 for adsorption and were then treated with a series of NaNO3stripping solutions with concentration ranging from low to high, to desorb the pre-adsorbed Cu(II) from the soils. 【Method】In this study, the two variable charge soils were pretreated with electrodialysis and then subjected to a series of adsorption and desorption tests with varying pH in an attempt to characterize copper ion (Cu(II)) desorption from clay minerals.【Result】Similar to the findings in the studies on kaolinite, Cu(II) adsorption of the soils increased rapidly from 0.05 to nearly 1 in score value within the range of the pH set for this research (pH 3.0~6.3). No matter what concentration of the electrolyte used, all the adsorption score value curves could be fitted with Fischer equation and the degree of fitting reached as high as 0.996 or more. Also it was noteworthy to note that when adsorption occurred in de-ionized water or 0.1 mol•L-1 NaNO3 solution, the same in pH, Cu(II) adsorption was always higher in de-ionized water than in 0.1 mol•L-1 NaNO3 solution in score value, which was attributed to the effect of the high concentration of electrolyte in the solution inhibiting Cu(II) adsorption. The findings of this experiment indicate, 1) that the adsorbed copper ions can be desorbed in de-ionized water and the desorption will decline in score value with desorption going on round after round in the waters the same in pH; 2) that in most cases, pH of the equilibrium liquid remains basically the same, around pH5.0, when the desorption lowers down to almost zero in score value; and 3) that the phenomena of re-adsorption will occur during the first round of desorption in de-ionized water only with pH above a specific pH, when the soils are pre-treated in 0.1 mol•L-1 NaNO3 solution, which means the copper ions will be adsorbed rather than desorbed when the equilibrium liquid is above this specific value in pH. Compared to Ali-Haplic Acrisol, Hyper-Rhodic Ferrasol is much lower in Cu(II) re-adsorption threshold. Similar to what happens in kaolinite, the results of sequential Cu(II) desorptions with NaNO3 solutions varying in concentration from low to high after the soils that had been pre-treated in either de-ionized water or 0.1 mol•L-1 NaNO3 solution, were subjected to three rounds of desorption with de-ionized water demonstrate 1) that Cu(II) that could not apparently be desorbed by de-ionized water, can be desorbed by NaNO3solution, and all the score value curves of pH-desorption follow a trend of rising first and then declining with rising pH regardless of concentration of NaNO3 or rounds of desorption; 2) that the score value of Cu(II) desorption peaks in 0.1 mol•L-1 NaNO3 solution; and 3) regardless of the concentration of NaNO3, there is a relatively gradual rise process before the desorption begins to soar up in score value. In all the case, Ali-Haper Acrisol is higher than Hyper-Rhodic Ferrasol in Cu(II) desorption score value, and in most cases the desorption score value curve has an apparent turning point where the desorption score value abruptly soars up, regardless of concentration of NaNO3 and rounds of desorption. Although the desorption equilibrium suspensions are not consistent in pH at the turning points, however, the pH at the turning points corresponding to the pHch of the desorption equilibrium suspensions are quite consistent, lingering around a special pH, that is, pH3.5, for Cu(II) adsorbed in de-ionized water, and pH3.18 or pH3.39 for CU(II) adsorbed in 0.1 mol•L-1 NaNO3 solution, which means that the copper ions adsorbed near the turning points of the pH-adsorption curves under any adsorption conditions exhibit a similar tendency in the desorption tests, that is climbing gently first and then abruptly soaring up with rising pH of the system. 【Conclusion】All the above-descrobed phenomenon and differences can be attributed to the difference between the two variable charge soils in content of iron oxide and the difference between iron oxide and kaolinite in nature of the surface charge.

Abstract:Soil organic phosphate (OP) is an important fraction of phosphorus in the soil environment. Its reactions in interfaces of the environment affects transport, transformation, bioavailability and environmental behaviors of phosphorus. This paper is a review that summarizes (1) reaction characteristics of adsorption-desorption and dissolution-precipitation of typical OPs on the surface of soil minerals and their microscopic mechanisms, and (2) environmental impacts, i.e., effects of the interaction between OPs and soil minerals on the speciation of OPs, interfacial reactions of metal ions, and colloidal chemical stability and dissolution-transfomation of the minerals. Soil OPs generally contain multiple phosphate groups and have large relative molecular mass and high charge density. OPs could interact strongly with environmental minerals through interfacial reactions, which affects the charge properties of minerals, adsorption characteristics of co-existing metal ions, and colloidal chemical stability of minerals. Interfacial reactons of OPs and their mechanisms are affected by a number of factors, such as type and crystallinity of the mineral, relative molecular mass of OP, pH, temperature, and coexisting ions. Sorption density of OP on the surface of minerals generally decreases with increasing pH of the system, crystallinity of minerals, and relative molecular mass of OP. OPs may generally form inner-sphere complexes (hydrogen bonding interactions also plays a role in some cases) on the surfaces of minerals, and surface complexes can even transform to surface precipitates. The adsorption of OP and metal ions on mineral surface generally has certain synergistic effects, especially under low pH conditions, i.e., metal ions promote the adsorption of OP and vice versa; adsorption mechanisms vary with reaction system, including mainly formation of ternary surface complexes and surface precipitates, and in most cases simultaneously involve multiple ones. In the end of the paper, discussion is conducted on main research hotspots and directions for future researches related to interaction between OP and minerals in the environment.

Abstract:【Objective】In soils iron oxides often congregate with lamellar phyllosilicates into various complex-like structures, thus generating significant impacts on physical and chemical properties of the soils. Phosphorus is an essential nutrient for growth of organisms in ecosystems, but may lead to eutrophication and deterioration of water quality, once it accumulates excessively in the soils. In soils phosphorus tends to be adsorbed onto minerals, and hence its mobility and bioavailability is significantly affected. Its adsorption by iron oxide-phyllosilicates associate differs from that by iron oxides and phyllosilicates separately in behavior. Yet, little has been done to explore effects of iron oxides-montmorillonite complex on speciation and bioavailability of phosphorus in soils. 【Method】In this paper, Montmorillonite-goethite complex (Mt-Goe) and complex of montmorillonite with amorphous or poorly crystalline iron oxides (Mt-HFO) were prepared, separately, and analyzed for structure, surface properties and features of adsorbing phosphate (Pi) and myo-inositol hexakisphosphate (IHP). 【Result】In Mt-Goe a small amount of hydroxyiron ions entered into the layers of montmorillonite, thus expanding the interlayer space, while montmorillonite was covered with goethite particles on the surface. In Mt-HFO, Fe3+ in-between the layers of monymorillonite hydrolyzed into hydroxy iron oxide and formed a layer of amorphous iron oxides on the surface of monymorillonite. The specific surface area of montmorillonite, Mt-Goe and Mt-HFO was 258.7, 185.4 and 226.4 m2 ?g-1 respectively, with surface fractal, isoelectric point and surface hydroxyl contents being on a rising order; and when pH was 5.5, the surface Zeta potential of the three was -46.1, -13.6 and -19.4 mV respectively. Pi and IHP adsorptions on the three types of samples were all dominated by homogeneous surface mono-layer adsorption. In terms of Langmuir saturated adsorption (qmax) and adsorption affinity, the three samples followed a decreasing order of Mt-HFO > Mt-Goe > montmorillonite. The pseudo-second-order kinetic model could be used to well fit Pi and IHP kinetic adsorption processes of the three samples, with adsorption rate constant following an order of Mt-HFO > Mt-Goe > montmorillonite. Compared to Pi, IHP was significantly lower in adsorption kinetic rate constant on the three samples, but significantly higher in qmax, and particularly low in adsorption rate on Mt-HFO, but much higher in qmax. 【Conclusion】Compared to montmorillonite, Mt-Goe and Mt-HFO are both lower in Pi and IHP adsorption rate, but higher in adsorption capacity. Among the two complexes, Mt-HFO is lower in Pi and IHP adsorption rate, but higher in adsorption capacity. All the three types of samples, montmorillonite, Mt-Goe and Mt-HFO, are lower in IHP adsorption rate than in Pi one, but much higher in IHP adsorption capacity than in Pi one.

Abstract:【Objective】The purpose of this article is to study mineral composition and cation exchange capacity (CEC) of the colloids and non-colloids in the two red soils collected from Hunan and Hainan provinces, separately, and adsorption behavior of Cu(II), Cd(II) and Pb(II)on thecolloids and non-colloids, too.【Method】 Soil colloidal and non-colloidal fractions were separated from bulk soils using sedimentation method, where particles in the upper portion of the suspension are collected as colloids at fixed time intervals after stirring. X-ray diffraction analysis was performed to determine mineral compositions of the colloids and non-colloids in the red soils. Free Fe and Al oxides were extracted with the DCB method and determined using ICP-AES. The batch method was used to investigate adsorption and desorption of Cu(II), Cd(II) and Pb(II) on and from soil colloids and non-colloids. Un-buffered salt of 1.0 mol L-1 NaNO3 was used to desorb pre-adsorbed heavy metals from soil colloids and non-colloids. 【Result】X-ray diffraction analysis shows that the colloids in the two red soils were composed mainly of secondary minerals with 1:1-typed kaolinite in dominancy and little of primary minerals.The contents of 2:1 typed minerals, such as vermiculite and hydro-mica in the soil colloids decreased with increasing soil development degree, while the content of kaolinite changed oppositely. The non-colloids in the two red soils contained mainly quartz and some other primary minerals.Soil Fe and Al oxides accumulated mainly in the soil colloids. The contents of free Fe and Al oxides were much higher in the soil colloids than in the soil non-colloids. For example, the content of free Fe oxide was as high as 78.03 g kg-1 in the colloids and only 9.93 g kg-1 in the non-colloids of the red soil from Hunan. The colloids in the two red soils were also much higher than, or 12 times as high as the non-colloids of the soils in CEC. The isothermal adsorption experiment indicates that the colloids were significantly higher than the non-colloids in adsorption capacity and affinity for Cu(II), Cd(II) and Pb(II), and the colloids of the red soil from Hunan was higher than those of the red soil from Hainan in adsorption capacity, which was consistent with mineral composition and CEC of the colloids of the two red soils. Cd(II) was adsorbed by soil colloids and non-colloids mainly through electrostatic attraction, however both electrostatic and non-electrostatic adsorptions were important mechanisms contributing significantly to adsorption of Cu(II) and Pb(II) on soil colloids and non-colloids. 【Conclusion】The secondary minerals and Fe/Al oxides are mainly distributed in the colloids of the two red soils. The colloids are much higher than the non-colloids in the two red soils in CEC, and hence in adsorption capacity and affinity for these heavy metals.