镧改性生物炭在砂柱中单独运移及与Cr(Ⅵ)共运移

Transport of single La-modified biochar in a sand column and its co-transport with Cr(Ⅵ)

为探究稀土金属改性生物炭在土壤-地下水中的运移行为,本研究选择常见稀土元素镧制备改性生物炭,并经球磨后制成镧改性生物炭细颗粒(La-BC),采用柱实验分别从流速、pH、离子强度和腐植酸浓度4个方面来研究La-BC单独运移和与Cr(Ⅵ)共运移时其在饱和均质石英砂介质中的运移和滞留规律。研究表明:流速从1.0 mL·min^(-1)增至1.5 mL·min^(-1)时,单独运移实验出流液中La-BC的质量回收率由58.0%增至73.4%,共运移实验出流液中La-BC的质量回收率为78.7%~80.1%。pH从5升至7时,La-BC单独运移及共运移时的穿透曲线的相对浓度(Ct/C0)峰值分别从0.66增至0.93和从0.80增至0.85。离子强度增至5 mmol·L^(-1)时,La-BC单独运移时的Ct/C0峰值降低至0.05,与Cr(Ⅵ)共运移时La-BC的穿透峰值为0.81~0.75。腐植酸浓度由0增至10 mg·L^(-1)时,La-BC单独运移及与Cr(Ⅵ)共运移时出水中La-BC质量回收率分别减少了约13个和3个百分点。相较于La-BC单独运移,共运移中Cr(Ⅵ)的存在除了在中性实验条件下抑制La-BC运移能力外,其余实验条件下皆促进了La-BC在饱和介质中的运移。因此,较低的流速、较低的pH环境、一定的离子强度及腐植酸浓度有助于改性生物炭的滞留稳定。

In order to investigate the transport of rare earth metal-modified biochar in soil-groundwater,lanthanum,a common rare earth element,was used to prepare modified biochar in this study.The lanthanum-modified biochar was then ball-milled to obtain fine biochar particles(La-BC).The transport and retention of La-BC alone(single-transport),and together with Cr(Ⅵ)(co-transport),in a saturated quartz sand column were studied at different conditions of flow rate,pH,ionic strength,and humic acid concentration.The results showed that the mass recovery of La-BC in the effluent increased from 58.0%to 73.4%in single-transport and ranged from 78.7%to 80.1%in cotransport when flow rate was increased from 1.0 mL·min^(-1)to 1.5 mL·min^(-1).The peak relative concentration(Ct/C0)values of La-BC breakthrough curves in single-transport and co-transport increased from 0.66 to 0.93 and from 0.80 to 0.85 when pH increased from 5 to 7.The peak Ct/C0 values of La-BC breakthrough curves were reduced to 0.05 in single-transport when ionic strength increased to 5 mmol·L^(-1),and to 0.81-0.75 in co-transport.The mass recovery in the effluent was reduced by about 13 percentage points and about 3 percentage points in single-transport and co-transport when humic acid concentration increased from 0 to 10 mg·L^(-1).Compared with single-transport,the existence of Cr(Ⅵ)in co-transport inhibited transport of La-BC under neutral conditions in a saturated medium and promoted its transport under other experimental conditions.Therefore,appropriately low flow rate,low pH,a certain ionic strength,and humic acid concentration contribute to the retention and stabilization of the modified biochar.