Turnover of soil organic carbon (SOC) is strongly affected by a balance between mineral protection and microbial degradation. However, the mechanisms controlling the heterogeneous and preferential adsorption of different types of SOC remain elusive. In this work, the heterogeneous adsorption of humic substances (HSs) and microbial carbon (MC) on a clay mineral (nontronite NAu-2) during microbial-mediated Fe redox cycling was determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results revealed that HSs pre-adsorbed on NAu-2 would partially inhibit structural modification of NAu-2 by microbial Fe(III) reduction, thus retarding the subsequent adsorption of MC. In contrast, NAu-2 without precoated HSs adsorbed a significant amount of MC from microbial polysaccharides as a result of Fe(III) reduction. This was attributed to the deposition of a thin Al-rich layer on the clay surface, which provided active sites for MC adsorption. This study provides direct and detailed molecular evidence for the first time to explain the preferential adsorption of MC over HSs on the surface of clay minerals in iron redox processes, which could be critical for the preservation of MC in soil. The results also indicate that ToF-SIMS is a unique tool for understanding complex organic−mineral−microbe interactions.
Removal of arsenic ion from fish condiment using lignin as adsorbent was investigated. The effects of pH of aquatic condiment solution, temperature, adsorption time, solid to liquid ratio, salt concentration and amino acid concentration on the removal ratio of arsenic ion from aquatic condiment were also studied. Removal ratio of arsenic ion reached 98.65% with pH 2, temperature 40 °C, adsorption time 25 min, solid to liquid ratio 1:70. It was confirmed that lignin can be used to remove arsenic ion from aquatic condiment.
Sulfhydryl lignin was prepared by immobilizing sulfhydryl onto wood lignin. The effect of pH, temperatμre, adsorption time, salinity of condiment and amino acid concentration of condiment on the adsorption behavior of sulfhydryl lignin was investigated, respectively. The adsorption kinetics and thermodynamics of Cu(Ⅱ) were also studied.
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