[Effect of Adding Compound Adsorbent on Phenanthrene and Cr(Ⅵ) Absorption by Lou Soil]

Abstract

To study the effect of the addition of compound adsorbent on the phenanthrene and Cr(Ⅵ) adsorption of Lou soil, biochar (made from corn stover) and B_200B (Bentonite modified by BS-12, dodecyl dimethyl betaine with modified ratio of 200% CEC of Bentonite) were mixed at mass ratios of 1:2, 1:1 and 2:1 as the compound adsorbents (CS_1:2, CS_1:1 and CS_2:1). Different amounts (2%, 5% and 10%) of these three compound adsorbents were added into Lou soil. Batch method was used to analyze the phenanthrene and Cr(Ⅵ) adsorption isotherms of different Lou samples, and compare the effect of environmental conditions such as pH value and temperature on the phenanthrene and Cr(Ⅵ) adsorption. The results indicated: ① Adsorption amounts of Cr(Ⅵ) on different Lou samples were 3.02 to 13.61 times higher than CK (original Lou soil). Under the same adding conditions (amount), Cr(Ⅵ) adsorption showed the order of CS_2:1 Lou > CS_1:1 Lou > CS_1:2 Lou > CK. Cr(Ⅵ) adsorption was a spontaneous process with decreased enthalpy (except CS_1:2) and increased entropy. Adsorption amounts of phenanthrene on different Lou samples were 3.87 to 13.00 times higher than CK. Phenanthrene adsorption presented the ranking of CS_1:2 Lou > CS_2:1 Lou > CS_1:1 Lou > CK at the adding amounts of 2% and 5%, while showed the order of CS_1:2 Lou > CS_1:1 Lou > CS_2:1 Lou > CK when 10% of the compound adsorbent was added. The adsorption was also a spontaneous process with decreased enthalpy and increased entropy. ② When the temperature was 10-30℃, the adsorption amount of Cr(Ⅵ) increased by 5.84%, 4.63% and 8.22% on CK, CS_1:1 and CS_2:1 Lou soils, and reduced by 2.70% on CS_1:2 Lou soils. Adsorption amount of phenanthrene increased by 1.69% of CK and reduced by 10.55%, 4.36% and 12.81% of CS_2:1, CS_1:1 and CS_1:2 Lou soils respectively. ③ When the pH was 4-10, the Cr(Ⅵ) adsorption had no significant change for CK, while those for CS_1:2, CS_1:1 and CS_2:1 Lou soils all reduced. Phenanthrene adsorption of CK, CS_1:2 and CS_1:1 Lou soils was all highest at pH=4, and phenanthrene adsorption of CS_2:1 Lou was highest at pH=7.④ The higher the ratio of B_200B in compound adsorbent, the better the phenanthrene adsorption was. The higher the ratio of biochar in compound adsorbent, the better the Cr(Ⅵ) adsorption was.

Keywords: Cr(Ⅵ); Lou soil; adsorption amount; biochar; modified bentonite; phenanthrene.