43~ 17ka川东北石笋~(234)U/~(238)U变化及其意义初探

铀(U)是自然界中最重的天然元素。U的价态随氧化-还原条件的变化而变化:在还原环境下多形成难溶于水的+4价铀离子沉淀,而在氧化环境中多形成易溶于水的+6价铀酰离子[UO_2]~(2+)随溶液迁移,并易与碳酸根离子(CO_3~(2-))、磷酸根离子(P0_4~(3-))和氟离子(F~-)形成络合离子。岩溶地下水由于具有较高的CO_2分压(pCO_2)和pH 值,铀酰离子主要以碳酸根离子络合态的形式存在。在表生环境下,土壤氧化还原状态(Eh)与土壤水分含量密切相关,水分含量降低有利于氧化环境形成和土壤Eh上升,因而有利于U的迁移。氧化还原状态也会影响U的同位素组成(~(234)U/~(238)U)。一些研究发现石笋~(234)U/~(238)U和生长速率之间存在明显关系,而石笋的沉积和生长速率又与气候环境尤其是降水量变化密切相关。此外,来源也是影响岩溶洞穴沉积~(234)U/~(238)U变化的重要因素。因此,石笋的U含量(或U/Ca比)和~(234)U/~(238)U是研究过去气候环境变化的重要指标。</p

响应面优化组氨酸改性蒙脱土脱除花生油中 黄曲霉毒素B1工艺Optimization of removal of aflatoxin B1 from peanut oil with histidine modified montmorillonite by response surface methodology

为了提高组氨酸改性蒙脱土（His-MMT）脱除花生油中黄曲霉毒素B1（AFB1）的效率，在单因素实验的基础上采用响应面法对His-MMT脱除花生油中AFB1的工艺条件进行优化，并分析His-MMT吸附前后花生油的品质变化情况。结果表明：His-MMT脱除花生油中AFB1的最佳工艺条件为His-MMT添加量0.17%、吸附温度110 ℃、吸附时间22 min，在此条件下花生油中AFB1含量从(58.26±0.48)μg/kg降低到(1.05±0.07) μg/kg，脱除率为(98.20±0.11)%；His-MMT吸附后花生油的红值由7.0下降至5.0，酸值（KOH）由（0.90±0.02）mg/g下降至（0.86±0.01）mg/g，总生育酚和总甾醇的保留率分别为85.85%和 97.26%。综上，His-MMT不仅可以高效脱除花生油中的AFB1，且对花生油的品质影响较小，在花生油精炼中具有较大的应用潜力。To improve the efficiency of removing aflatoxin B1 (AFB1) from peanut oil by histidine modified montmorillonite(His-MMT), response surface methodology was used to optimize the removal conditions of AFB1 from peanut oil by His-MMT based on single factor experiment, and the quality change of peanut oil before and after adsorption was studied. The results showed that the optimal conditions for AFB1 removal were obtained as follows: dosage of His-MMT 0.17%, adsorption temperature 110 ℃ and adsorption time 22 min. Under these conditions, the AFB1 content in peanut oil decreased from (58.26±0.48) μg/kg to (1.05±007) μg/kg, and the removal rate was (98.20±011)%. After adsorption, the red value of peanut oil decreased from 7.0 to 5.0, the acid value decreased from (0.90±0.02) mgKOH/g to (086±0.01) mgKOH/g, and the retention rates of total tocopherol and total sterol were 8585% and 9726%, respectively. In conclusion, His-MMT can not only efficiently remove AFB1 from peanut oil, but also has little effect on the quality of peanut oil. His-MMT has great application potential in the refining of peanut oil