| The term "aging" describes the process by which the extractability, exchangeability, bioavailability, and/or toxicity of copper added to soils decrease with contact time. This process is sometimes also termed "natural attenuation". Obviously, there is great difference in bioavailability and/or toxicity of copper between field soils and freshly spiked soils, thus, it is very important and necessary to understand and predict the aging process in the context of ecological risk assessment and drawing soil quality criterion. Moreover, the study on aging of added Cu helps to supply some new experimental evidence to understand correctly the chemical behaviors of copper in soils, and to enrich and develop soil chemistry and soil surface chemistry. In addition, it helps also to guide the management and remediation of contaminated soils.In this experiment, the aging process and mechanism of copper added to bentonite, the aging process of copper in the systems of bentonite, and the effects of pH, temperature and organic acids on the aging of added Cu were deep studied using sequential extraction procedure and X-ray diffraction technique. The objectives were to supply evidence to micropore diffusion for aging of copper added to clay mineral, and to discover the the effects of organic acids, temperature and pH on long-term aging of added Cu, and explain their difference in clay mineral and oxide. Only this, the chemical behaviors of copper in soils could be controlled and adjusted effectively.Some important results gained were described as follows:(1) The aging of copper added to bentonite was a very slow reaction which lasting for more than one year. It was mainly controlled by micropore diffusion reaction, with apparent diffusion rate coefficient (D/r2) of 7.44×10-11～2.31×10-10 s-1. With pH the changes occurred of ionic species of diffusion into interlayer of clay mineral, where at lower pH (<5.5), the diffusion ion was Cu2+, but at higher pH (7.68), CuOH+ became the dominating ion of diffusion. So, the hypothesis about aging process of added Cu was validated and the theory of soil surface chemistry was enriched.(2) Humic acid, goethite, and calcium carbonate all accelerated greatly the short-term aging of added Cu (the increase in the value of M), due to surface nucleation/precipitation. However, they inhibitted the long-term aging process (micropore diffusion), especially calcium carbonate (the significant decrease in apparent diffusion rate coefficient), which was ascribed to the complexation between these soil components and added copper who would block the diffusion of copper ion into interlayer of clay mineral. Thus, it supplied new evidence to understand the chemical behaviors of heavy metals in soils, especially calcareous soils.(3) In clay mineral (bentonite), humic acid significantly accelerated the aging of added Cu, and there was not effect for low-molecular organic acids (EDTA and oxalate acid). While, in oxide (goethite), humic acid and EDTA all significantly reduced the aging reaction, and oxalate acid has no effect on the aging process. For two minerals, the rise in temperature markedly promoted the aging of added Cu; however, the change of pH has not evidentedly effect on it. Generally, The effects of these factors on aging of copper added to goethite was greater than that to bentonite, which suggested that the aging process of heavy metals in variable-charge soils such as red soil, latosol, etc., was more easily adjusted and controlled, in other words, the aging reaction was more unstable. Obviously, it could scientifically guide to adjust directionally the chemical behaviors of copper in soils.
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