Zn^(2+)和Mn^(2+)处理水钠锰矿后对Pb^(2+)吸附量的影响

Effects on Pb^(2+) adsorption capacity of birnessite treated with Zn^(2+) and Mn^(2+)

分别采用Zn2+和Mn2+处理锰平均氧化度较高的水钠锰矿,对比研究了经不同浓度的Zn2+和Mn2+处理后矿物的锰平均氧化度、d110面网间距、对Pb2+的最大吸附量以及吸附过程中Zn2+和Mn2+的最大释放量等的变化.同时,通过Zn2+和Mn2+与水钠锰矿表面反应行为的不同,进一步明确矿物结构中的八面体空穴数量与重金属吸附量的关系.研究结果表明,水钠锰矿经Zn2+和Mn2+分别处理后,矿物类型未改变,并具有相似的晶体形貌.Zn2+溶液处理水钠锰矿时,随着Zn2+浓度的增大,水钠锰矿的锰平均氧化度和d110面网间距不变,说明结构中空穴数量未改变,Zn2+通过占据部分吸附点位,导致其对Pb2+的最大吸附量从3190mmo.lkg-1减少为2030mmol.kg-1.而Mn2+溶液处理水钠锰矿时,大多数Mn2+被氧化为Mn3+,这些Mn3+部分位于八面体空穴上下方的吸附位点,部分进入八面体空穴中.随着加入的Mn2+浓度增大,Mn2+被氧化为Mn3+而进入八面体空穴的数量增多,锰平均氧化度减小,d110面网间距从0.14160nm增大至0.14196nm,说明结构中空穴数量减少,对Pb2+的最大吸附量从3190mmol·kg-1减少至1332mmo·lkg-1.对比研究结果表明,水钠锰矿结构中的八面体空穴数量对Pb2+的吸附量的大小起着非常重要的作用.

The Pb^2＋ adsorption behavior of birnessite with high Mn average oxidation state （AOS） before and after treatment by preadsorption of Zn^2＋ and Mn^2＋ was compared. The association of vacant Mn octahedral sites with Pb^2＋ adsorption was determined from the AOS, d（110）-interplanar spacing, maximum Pb^2＋ adsorption, and maximum Zn^2＋ and Mn^2＋ release during Pb^2＋ adsorption by the birnessites before and after treatment. The AOS and d（110） -interplanar spacing of the birnessites remained almost unchanged as the concentration of Zn^2＋ increased, indicative of an unchanged number of vacant Mn octahedral sites. Maximum Pb^2＋ adsorption decreased from 3190 to 2030 mmol·kg^-1 due to Zn^2＋ occupancy of the adsorption sites. When the concentration of Mn^2＋ in the pretreatment increased from 1 to 2.4 mmol·L^-1, the AOS of the birnessites decreased, and most of the Mn^2＋ was oxidized to Mn^3＋ located above or below vacant Mn octahedral sites or migrated into vacant Mn octahedral sites. The d（110） -interplanar spacings of the treated birnessites increased from 0. 14160 to 0. 14196 nm, indicative of a decrease in the number of vacant Mn octahedral sites, mainly due to the produced Mn^3＋ migrating into vacant Mn octahedral sites. Moreover, the maximum Pb^2＋ adsorption of the Mn^2＋ - treated birnessites was observed to decrease from 3190 to 1332 mmol·kg^-1. The results suggest that birnessite Pb^2＋ adsorption capacity is largely determined by the number of Mn site vacancies.