酸性水稻土pH缓冲容量提升与Cd等重金属钝化效果的持续性

The pollution of paddy soils by heavy metals resulted in Cd-contaminated rice in south of China, which attracted public attention greatly. In addition to high contents of heavy metals in the soils, soil acidification is another important reason for Cd-contaminated rice. At present, amendments are normally applied to increase soil pH and immobilize heavy metals in the paddy soils. However, the long-term effectivity of the remediation method should be highly related with soil pH buffering capacity (pHBC). In this project, the buffering ability of paddy soils derived from red soil to acidity is chosen as a key factor for immobilization of heavy metals in the soils. The relationship of pHBC of paddy soils with pH variation and transformation of chemical forms of heavy metals will be investigated when paddy soils change from submerging to draining. Crop straw biochars will be used to increase soil pHBC and the effect of increasing pHBC on immobilization of heavy metals in the soils will be examined. The new methods will be developed to increase functional groups on the biochars to prepare highly efficient amendments through surface modification and self-assembling of organic compounds on the biochars. The effectiveness of modified biochars in increasing soil pHBC and sustainability of heavy metal immobilization in the soils will be examined. The mechanisms for the increasing sustainability of heavy metal immobilization in paddy soils induced by biochars and modified biochars will be elucidated through the series of experimental works. The findings of the project will enrich soil acidification theory and provide useful reference for the new methods developed for long-term immobilization of heavy metals in acidic paddy soils, which is significant for the Rural Revitalization Strategy and public health.

我国南方稻田土壤受重金属污染导致部分地区出现稻米镉含量超标，引起广泛关注。除重金属含量外，红壤性水稻土高酸度也是镉米产生的主要原因。目前主要采用施改良剂提高土壤pH并钝化重金属的修复方法。该方法修复效果的长效性应受土壤pH缓冲容量的影响。本项目以红壤性水稻土的酸缓冲性能为核心，研究土壤pH缓冲容量与干湿交替过程中土壤pH变化和重金属形态转化的关系、秸秆生物质炭提高土壤pH缓冲容量的效果及对重金属钝化的长效性的影响，研究生物质炭表面改性及官能团扩增技术以制备高效土壤改良剂，验证这种高效改良剂提升土壤pH缓冲容量及增加土壤重金属钝化持续性的效果，阐明秸秆生物质炭及表面改性和官能团扩增生物质炭提升重金属钝化效果持续性的机制。研究结果将丰富土壤酸化理论，并为酸性水稻土中重金属长效钝化技术的研发提供理论依据和技术支撑，对实施“乡村振兴战略”和保障民众的身体健康具有重要的实际意义。

我国南方稻田土壤受重金属污染导致部分地区出现稻米镉含量超标，引起广泛关注。红壤性水稻土落干过程中pH显著下降导致Cd活化是镉米产生的重要原因。本项目以红壤性水稻土的酸缓冲性能为核心，研究了土壤pHBC与干/湿交替过程中土壤pH变化和重金属形态转化的关系、秸秆生物质炭提高土壤pHBC的效果及对重金属钝化的长效性的影响，研究了生物质炭改性及官能团扩增以及改性生物质炭对土壤pHBC提升效果及对土壤Cd钝化效果，阐明秸秆生物质炭及改性生物质炭提升重金属钝化效果的机制。结果表明土壤CEC是决定水稻土pHBC的关键因子，淹水过程中3价铁的还原对质子的消耗远远大于锰氧化物和硫酸盐的还原，是淹水过程中土壤pH升高的主要原因。淹水和落干处理导致的土壤pH先升后降是有效态Cd先降后升的主要原因。土壤pHBC通过影响干/湿交替过程中土壤pH的变化幅度影响有效态Cd含量的变化。添加生物质炭不仅提高了土壤pH和pHBC，还降低了土壤有效态Cd的含量。生物质炭提高水稻土pHBC，从而抑制落干过程中土壤pH的下降和有效态Cd的增加，不同生物质炭抑制效果的大小顺序为：向日葵盘炭>花生秸秆炭>玉米秸秆炭。过氧化氢和浓硝酸/浓硫酸混合酸改性均有效增加了稻草炭表面羧基数量及质子结合位点数，因此添加改性生物质炭可以更有效提升土壤pHBC，抑制水稻土落干过程中土壤pH下降和有效态Cd的增加，混合酸改性生物质炭的抑制效果更佳。壳聚糖和海藻酸盐改性可以有效扩增稻草炭的官能团数量，添加官能团扩增生物质炭提高了酸性水稻土的pHBC，减缓了水稻土落干期间pH的下降和有效态Cd的增加。壳聚糖改性生物质炭提升土壤pHBC的效果优于海藻酸盐改性生物质炭，但后者抑制Cd活化的效果优于前者。研究结果将丰富土壤酸化理论，并为酸性水稻土中重金属长效钝化技术的研发提供理论依据和技术支撑，对实施“乡村振兴战略”和保障民众健康具有重要意义。