Charge characteristics and related dispersion/flocculation behavior of soil colloids as the cause of turbidity

Effect of an allophanic soil on humification reactions between catechol and glycine: Spectroscopic investigations of reaction products

“…The pH of the sample was slightly acidic (pH 6.27 for H 2 O; pH 5.10 for 1 M KCl), indicative of a solid acid. The CEC (7.8 cmol kg À1 ) and SSA (106 m 2 g À1 ) for our sample were lower than values previously reported for allophanes (e.g., 11-25 cmol kg À1 for CEC and 160-580 m 2 g À1 for SSA) [23,24,29]. These results suggest that the allophanic soil used in the present study is a mixture of allophane and other minerals.…”

“…The molar ratio of SiO 2 /Al 2 O 3 for the allophanic soil in the present study was calculated to be 1.52, which is consistent with values reported for allophanes (1.0-2.0) [23][24][25]. In addition, the allophanic soil contained 2.8% iron oxides.…”

“…Short-range allophanes widely distribute in volcanic soils. Allophanic soil has a relatively large surface area, ranging from 100 to 170 m 2 g À1 , and a slightly acidic isoelectric point [21][22][23][24][25][26]. These properties suggest that allophanic soil may be an effective catalyst for humification reactions between phenols and amino acids.…”

Variations in the cation exchange capacity of a ferralsol supplied with vinasse, under changing aeration conditions

“…The CEC of halloysite depends on its hydration (the CEC of halloysite 2 H 2 O and halloysite 4 H 2 O range between 5-10 and 40-50 cmol c kg − 1 , respectively (Rhoades, 1982)), and on isomorphic substitution of Si(IV) by Al(III) which leads to more permanent charges than in kaolinite (Tari et al, 1999). This may explain why Joussein et al (2005) noted a lower contribution of pH dependent charges to halloysite CEC than to kaolinite CEC, and why Itami and Fujitani (2005) found almost no variations in halloysite CEC relative to pH. In addition, the decreases in ξ-potential of halloysite and kaolinite were observed at pH values of less than 6 and more than 10 (Tari et al, 1999), suggesting no or minor variations in clay negative charge and CEC with pH between 5 and 7, as in this study.…”

The effects of soil properties on the turbidity of catchment soils from the Yongdam dam basin in Korea

“…This range fell into the pH range reported for the turbid water layer in the Yongdam reservoir (Shin et al 2004). The charge characteristics and related dispersion behavior of a mineral are known to be substantially affected by solution pH (Itami and Fugitani 2005). In general, as the solution pH decreases, the mineral surface charges become more positive and the particles tend to aggregate more.…”