CN111790347A - 一种用于重金属铬污染土壤原位修复的单层矿物材料及其离子热辅助合成方法 - Google Patents
一种用于重金属铬污染土壤原位修复的单层矿物材料及其离子热辅助合成方法 Download PDFInfo
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Abstract
本发明涉及一种用于重金属铬污染土壤原位修复的单层矿物材料及其离子热辅助合成方法,所述单层矿物材料为单层MgAl水滑石,由单层纳米片团聚得到,单层纳米片尺寸为10~40nm,厚度为0.6~0.8nm,比表面积为180~230m2/g。本发明提供的S‑MgAl‑LDH材料比表面积大、吸附效果好,能快速吸附Cr(VI)并将其进行固定,吸附效率为83~96.33%,且无有毒物质析出、不产生二次污染,能在短时间内达到土壤修复的目的,对酸、碱性的土壤均有较好的修复效果,因此具有广阔的应用前景。
Description
技术领域
本发明涉及矿物吸附剂材料和重金属污染土壤修复技术领域,尤其涉及一种用于重金属铬污染土壤原位修复的单层矿物材料及其离子热辅助合成方法。
背景技术
随着社会经济与工农业的快速发展,铬作为一种典型的重金属元素被广泛应用于冶金、制革、电镀、印染、油漆、防腐、军工、饲料添加剂等行业,由此导致大量铬及其化合物进入土壤并使其遭受了严重污染。全国土壤环境状况总体不容乐观,部分地区土壤污染较重,耕地土壤环境质量堪忧,工矿业废弃地土壤环境问题突出。全国土壤总的超标率达到了16.1%,其中无机污染物超标点位数占全部超标点位的82.8%,铬作为主要无机污染物之一,其点位超标率为1.1%。据统计,我国存在镉、砷、铅、铬、汞等重金属污染问题的耕地面积多达2000万公顷,约占全国总耕地面积的1/5,每年因土壤重金属污染问题而减产粮食约1000 万吨。土壤重金属污染治理成为我国亟待解决的环境问题之一。
目前,重金属污染土壤的修复原理包括采用各种技术来清除污染土壤中的重金属元素或者降低其活性和有效态组分,以达到修复土壤的目的。铬作为土壤重金属污染中最典型的一个元素,通常以Cr(III)和Cr(VI)两种稳定价态存在,对其进行治理修复的途径有两种:一种是改变铬离子的存在形态,将毒性高、迁移能力强的Cr(VI)还原为毒性小、稳定性较强的Cr(III),以达到修复的目的;另一种是将铬直接从土壤中去除,使铬的留存浓度接近或达到土壤的背景值。基于这两种修复途径,铬污染土壤的修复技术主要有物理修复法、生物修复法、化学修复法等。其中,物理修复法主要有电动力学修复技术等,该技术虽可实现土壤中铬的分离,但是工程量大,造价高,且对土壤有一定要求,应用具有一定的局限性。化学修复法典型的有化学淋洗技术、化学还原技术等,化学淋洗技术通过淋洗污染土壤,使含六价铬的淋洗水进入地下水,再将含六价铬的地下水抽到地表进行处理,该方法虽然处理效果明显,但修复成本高、工程量大;化学还原技术是利用化学还原剂将污染物还原成难溶态,从而降低污染物的迁移性和生物可利用性,达到修复污染土壤的目的,该技术虽然修复时间短,效果好,但是药耗大、成本高,且大量化学药剂的使用,还会引起二次污染。生物修复法常利用植物、动物以及微生物吸收土壤中重金属,达到土壤修复的目的,该技术虽然实施较简单,成本低,但对环境的要求较高,且治理周期长、生物量小、效果不显著,不能治理重污染土壤。鉴于我国土壤铬污染的严重性,亟待开发一种经济、高效、实用的治理技术。
发明内容
本发明的目的在于,针对现有技术中的不足,提出一种对Cr(VI)吸附高效、低成本且环境友好型的单层矿物材料S-MgAl-LDH(单层MgAl水滑石)。
本发明的目的之二在于,提供上述S-MgAl-LDH的制备方法,该方法能高效地制备出单层纳米片型的LDH,并且操作简单,成本较低。
本发明的目的之三在于,提供上述S-MgAl-LDH在重金属铬污染土壤原位修复中的应用,以解决传统处理方法处理效率低、周期长、工程复杂等问题。
为实现本发明目的,本发明采用的技术方案为:
一种用于重金属铬污染土壤原位修复的单层矿物材料,所述单层矿物材料为单层MgAl水滑石,由单层纳米片团聚得到,单层纳米片尺寸为10~40nm,厚度为0.6~0.8nm,比表面积为180~230m2/g。水滑石化学式为[M2+ 1-xM3+ x(OH)2]x+[An-]x/n·m H2O,其中x通常取0.20~0.33,m代表层间水分子,没有特定的范围值, n代表阴离子的电荷数,通常取1或2。
一种用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,包括以下步骤:
1)将氯化胆碱与尿素加入预先装有超纯水的聚四氟乙烯反应釜中,在 60-80℃下进行搅拌使之溶解完全,制得DES离子溶液;
2)将Mg(NO3)2·6H2O、Al(NO3)3·9H2O加入步骤1)所得DES离子溶液中,搅拌至固体溶解,然后向体系中加入过量的KOH(摩尔量大于 2n(Mg2+)+3n(Al3+)),保持搅拌直至混合完全,随后将反应釜密封并置于烘箱中进行陈化反应,反应完成后取出反应釜,冷却后,将其中的反应液进行浓缩收集其中的白色沉淀物,经洗涤、离心,干燥,研磨得到S-MgAl-LDH粉末。
上述方案中,步骤1)中氯化胆碱与尿素的摩尔比为1:2,所述DES离子溶液中氯化胆碱浓度为130~210g/L。
上述方案中,步骤2)中Mg(NO3)2·6H2O、Al(NO3)3·9H2O的Mg:Al摩尔比为2~4:1,其中Mg(NO3)2·6H2O与氯化胆碱的摩尔比为1:10。优选的是, Mg(NO3)2·6H2O、Al(NO3)3·9H2O的Mg:Al摩尔比为2:1。
上述方案中,步骤2)搅拌至固体溶解的时间为3~10min。
上述方案中,步骤2)保持搅拌直至混合完全的时间为10~60min。
上述方案中,步骤2)中陈化反应温度为80~120℃,反应时间为36~48h。
上述方案中,步骤2)浓缩收集的方法为采用高速离心机进行离心,离心转速为6000~9000r/min,离心时间为2~5min。
一种上述单层矿物材料在重金属铬污染土壤原位修复方面的应用。
一种利用上述单层矿物材料对重金属铬污染土壤进行原位修复的方法,具体为:将S-MgAl-LDH先配置成浓度为2~20g/L的悬浮液,按悬浮液中S-MgAl-LDH 与土壤的比例为10~100g/Kg的量均匀施加到土壤中进行原位修复。
一种上述单层矿物材料在重金属铬污染水处理方面的应用。
本发明将LDH的原料置于DES离子溶液中进行反应,DES离子溶液作为一种离子反应的介质,为反应提供了独特的离子环境,可以通过调整浓度控制LDH 的成型大小并提高材料表面的理化性质,相较于传统的尿素法制备的LDH,本发明提供的LDH颗粒尺寸更小,比表面积更大,从而吸附能力更好(吸附过程中, Cr2O7 2-与水滑石层间的CO3 2-进行阴离子交换,且颗粒尺寸越小,比表面积越大,阴离子交换性能越好,吸附性能越好)。
本发明的有益效果是:
(1)本发明的S-MgAl-LDH材料比表面积大、吸附效果好,与传统的MgAl-LDH相比,吸附效率提升至83~96.33%,能快速吸附Cr(VI)并将其进行固定,且无有毒物质析出、不产生二次污染。
(2)制备方法操作简单,成本较低,能高效地制备出单层纳米片型的LDH。
(3)该修复技术适合处理重度铬污染土壤的原位修复,与其他修复方法相比,本材料制备方法简单、成本较低;且能在短时间内达到土壤修复的目的,对酸、碱性的土壤均有较好的修复效果,因此具有广阔的应用前景。
附图说明
图1为本发明对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH 的XRD图;
图2为对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH的SEM 图;
图3为实施例1所制备的S-MgAl-LDH的AFM图;
图4为实施例1所制备的S-MgAl-LDH延剖面线的横截面分析图;
图5为对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH吸附处理不同浓度含铬土壤的修复效果对比图;
图6为实施例1所制备的S-MgAl-LDH处理不同浓度含铬土壤的修复效果随时间的变化曲线图;
图7为实施例1所制备的S-MgAl-LDH处理高浓度含铬土壤时,Mg2+、Al3+溶出量随时间变化的曲线图;
图8为分别使用对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH 材料投加量对铬污染土壤的修复效果图;
图9为分别使用对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH 材料对不同pH值的铬污染土壤的修复效果图。
具体实施方式
为便于理解,下面结合具体实施例和附图进一步阐明本发明的内容,但本发明的内容不仅仅局限于下面的实施例。
对比例1
尿素法制备MgAl-LDH,具体步骤如下:称取1.54g的Mg(NO3)2·6H2O和 1.13g的Al(NO3)3·9H2O(Mg:Al摩尔比为2:1)和1.76g的尿素,并用50mL 的超纯水将三种固体完全溶解,之后将混合溶液转入聚四氟乙烯的反应釜中,加上金属外壳密封并置于100℃烘箱中反应48h,反应完成后取出反应釜,用自来水冷却后打开,将其中的反应液用高速离心机在8000rpm条件下离心5min,可得到其中的白色沉淀物,并用超纯水反复洗涤-离心3次,再将产物放在50℃烘箱中干燥,研磨后得到MgAl-LDH粉末。
实施例1
一种单层矿物材料S-MgAl-LDH,制备方法包括如下步骤:
1)称取8.38g氯化胆碱与7.07g尿素于预先装有50mL超纯水的聚四氟乙烯反应釜内胆中,在80℃恒温条件下进行磁力搅拌,制得DES离子溶液;
2)称取1.54g的Mg(NO3)2·6H2O和1.13g的Al(NO3)3·9H2O(Mg:Al摩尔比为2:1)加入到上述DES离子溶液中,持续搅拌5min,直至固体完全溶解,然后向反应釜中再加入1.69gKOH,80℃下持续恒温搅拌30min直至混合完全,随后将反应釜套上金属外壳密封并置于100℃烘箱中陈化反应48h,反应完成后取出反应釜,用自来水冷却后打开,将其中的反应液用高速离心机在8000rpm转速下离心5min,收集得到其中的白色沉淀物,用超纯水反复洗涤-离心3次,再将产物放在50℃烘箱中干燥过夜,研磨后可得到S-MgAl-LDH粉末材料。
图1为对比例1制备的MgAl-LDH与本实施例所制备的S-MgAl-LDH的XRD 图;图2(a)、(b)分别为对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH 的SEM图,由图可知,对比例1用传统尿素法合成的MgAl-LDH为正六边形层状结构,尺寸在1-2μm之间,而使用离子热辅助合成法制备的S-MgAl-LDH尺寸为纳米级,约为50nm以下。
图3和图4分别为本实施例所制备的S-MgAl-LDH的AFM图像及其延剖面线的横截面分析图,由图可知,S-MgAl-LDH为纳米片状结构团聚得到的颗粒物,单层纳米片尺寸为10~40nm,厚度为0.6~0.8nm。
经测试,本实施例所制备的S-MgAl-LDH粉末材料比表面积为213.14m2/g。
实施例2
本实施例采用室内试验,利用对比例1制备的MgAl-LDH与实施例1制备的 S-MgAl-LDH两种材料处理含不同铬浓度的土壤样品。
供试土壤为采自江苏省宿迁市未受污染土壤,采集后风干,过100目筛,密封储存于干燥器内备用,测定其pH值为6.21。将该土壤用分析纯重铬酸钾人为污染,制备铬污染土壤样品,使土壤中Cr(VI)的浓度分别为1g/Kg、2g/Kg、3g/Kg、 5g/Kg;取10mL离心管,分别向其中加入5mL超纯水与1g铬污染土壤样品,置于旋转混匀仪上在30rpm条件下处理90min,然后通过注射器与0.45μm的滤头抽取清液,用火焰原子吸收分光光度法测定清液中六价铬离子的浓度,分别为 22mg/L、48mg/L、70mg/L、152mg/L,以此浓度作为后续处理实验中Cr(VI)的初始浓度值。
再分别向10mL离心管中加入5mL超纯水、1g铬污染土壤样品(土壤中Cr(VI) 的浓度分别为1g/Kg、2g/Kg、3g/Kg、5g/Kg)以及0.01g LDHs材料(分别为对比例1制备的MgAl-LDH和实施例1制备的S-MgAl-LDH),置于旋转混匀仪上在30rpm条件下处理90min,测试清液中六价铬离子的浓度,以此评估该材料对重金属铬污染土壤的修复效果。
如图5所示为对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH 吸附处理不同浓度含铬土壤的修复效果对比图,处理相同程度铬污染土壤时, S-MgAl-LDH的修复效果明显比MgAl-LDH好,且随着铬污染程度的加深, MgAl-LDH的修复效果下降较明显,而S-MgAl-LDH的修复效果受到的影响相对较小,对Cr(VI)仍然有高于64%的去除率,说明S-MgAl-LDH可以修复重度污染的土壤。
实施例3
利用实施例1所制得的S-MgAl-LDH材料处理实施例2中制得的含不同铬浓度的土壤样品。
取10mL离心管,分别向其中加入5mL超纯水、1g铬污染土壤样品(土壤中Cr(VI)的浓度分别为1g/Kg、2g/Kg、3g/Kg、5g/Kg)以及0.01g S-MgAl-LDH 材料,置于旋转混匀仪上在30rpm条件下反应不同时间(10min、30min、60min、 90min、120min)之后进行取样,通过注射器与0.45μm的滤头抽取清液,用火焰原子吸收分光光度法测定清液中六价铬离子的浓度,以此评估S-MgAl-LDH材料对重金属铬污染土壤的修复效率。
如图6所示为实施例1所制备的S-MgAl-LDH处理含不同浓度铬土壤的修复效果随时间的变化曲线图,可以看出S-MgAl-LDH材料对1g/Kg的铬污染土壤的去除率在10min时就高达96%以上,随着处理时间增加去除率波动较小,而随着土壤中铬浓度的增加,对土壤的修复效率逐渐下降,土壤中铬浓度为5g/Kg时去除率约为63%,说明该材料对铬污染土壤修复效果良好。将土壤中铬浓度为5g/Kg 的铬污染土壤样品用S-MgAl-LDH材料吸附处理后溶液用火焰原子吸收分光光度法进行Mg2+、Al3+的含量测定,结果如图7所示,溶液中Mg2+和Al3+的含量在吸附处理过程中均接近于零,即在吸附反应过程中基本无Mg2+和Al3+的溶出,说明该方法处理铬污染土壤不会产生二次污染。
实施例4
利用对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH处理Cr(VI) 的浓度为5g/Kg、pH值为7的污染土壤,探究不同LDHs投加量对修复效果的影响。
向10mL离心管中依次加入5mL超纯水、1g铬污染土壤样品以及不同投加量(0.01g、0.03g、0.05g、0.07g)的MgAl-LDH与S-MgAl-LDH材料,置于旋转混匀仪上在30rpm条件下反应90min之后进行取样,反应条件与测量方式同实施例2。两种材料不同投加量对铬污染土壤的修复效果图结果如图8所示,可见两种材料对于Cr(VI)的去除率均随着投加量的增加而增加,但整体上 S-MgAl-LDH的修复效果要明显好于MgAl-LDH,甚至S-MgAl-LDH仅仅投加0.01g时的修复效果要比MgAl-LDH投加0.07g的效果要好。
实施例5
利用对比例1制备的MgAl-LDH与实施例1制备的S-MgAl-LDH处理Cr(VI) 的浓度为5g/Kg、不同pH值的污染土壤,探究土壤不同pH值对修复效果的影响。
向10mL离心管中依次加入5mL超纯水、1g铬污染土壤样品(pH值分别为 3、5、7、10)以及0.05g的MgAl-LDH(S-MgAl-LDH)材料,置于旋转混匀仪上在30rpm条件下反应90min之后进行取样,反应条件与测量方式同实施例2。两种材料在不同pH值下修复效果如图9所示,可见pH值对MgAl-LDH与 S-MgAl-LDH两种材料的修复效果均影响较小,其中S-MgAl-LDH的去除率均在 83%以上,在pH值为7时达到最高值96.33%,均明显高于MgAl-LDH的修复效果,说明此材料既可以处理酸性土壤也可以处理碱性土壤,在土壤修复方面具有广泛的适用性。
以上未涉及之处,适用于现有技术。
虽然已经通过示例对本发明的一些特定实施例进行了详细说明,但是本领域的技术人员应该理解,以上示例仅是为了进行说明,而不是为了限制本发明的范围,本发明所属技术领域的技术人员可以对所描述的具体实施例来做出各种各样的修改或补充或采用类似的方式替代,但并不会偏离本发明的方向或者超越所附权利要求书所定义的范围。本领域的技术人员应该理解,凡是依据本发明的技术实质对以上实施方式所作的任何修改、等同替换、改进等,均应包含在本发明的保护范围。
Claims (10)
1.一种用于重金属铬污染土壤原位修复的单层矿物材料,其特征在于,所述单层矿物材料为单层MgAl水滑石,由单层纳米片团聚得到,单层纳米片尺寸为10~40nm,厚度为0.6~0.8nm,比表面积为180~230m2/g。
2.一种权利要求1所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,包括以下步骤:
1)将氯化胆碱与尿素加入预先装有超纯水的聚四氟乙烯反应釜中,在60-80℃下进行搅拌使之溶解完全,制得DES离子溶液;
2)将Mg(NO3)2·6H2O、Al(NO3)3·9H2O加入步骤1)所得DES离子溶液中,搅拌至固体溶解,然后向体系中加入过量的KOH,保持搅拌直至混合完全,随后将反应釜密封并置于烘箱中进行陈化反应,反应完成后取出反应釜,冷却后,将其中的反应液进行浓缩收集其中的白色沉淀物,经洗涤、离心,干燥,研磨得到S-MgAl-LDH粉末。
3.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤1)中氯化胆碱与尿素的摩尔比为1:2,所述DES离子溶液中氯化胆碱浓度为130~210g/L。
4.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤2)中Mg(NO3)2·6H2O、Al(NO3)3·9H2O的Mg:Al摩尔比为2~4:1,其中Mg(NO3)2·6H2O与氯化胆碱的摩尔比为1:10。
5.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤2)搅拌至固体溶解的时间为3~10min。
6.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤2)保持搅拌直至混合完全的时间为10~60min。
7.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤2)中陈化反应温度为80~120℃,反应时间为36~48h。
8.根据权利要求2所述的用于重金属铬污染土壤原位修复的单层矿物材料的制备方法,其特征在于,步骤2)浓缩收集的方法为采用高速离心机进行离心,离心转速为6000~9000r/min,离心时间为2~5min。
9.一种利用权利要求1所述的单层矿物材料对重金属铬污染土壤进行原位修复的方法,其特征在于:将S-MgAl-LDH先配置成浓度为2~20g/L的悬浮液,按悬浮液中S-MgAl-LDH与土壤的比例为10~100g/Kg的量均匀施加到土壤中进行原位修复。
10.一种权利要求1所述的单层矿物材料在重金属铬污染水处理方面的应用。
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