镁改性硅藻土回收废水氮磷产物对水中Pb<sup>2+</sup>和Zn<sup>2+</sup>的去除

引用本文

吴盈秋, 夏鹏, 李远, 王学江. 镁改性硅藻土回收废水氮磷产物对水中Pb²⁺和Zn²⁺的去除[J]. 环境科学, 2022, 43(12): 5667-5675.

WU Ying-qiu, XIA Peng, LI Yuan, WANG Xue-jiang. Removal of Pb(Ⅱ) and Zn(Ⅱ) from Wastewater via Magnesium-Modified Diatomite Product Recovering Nitrogen and Phosphorus[J]. Environmental Science, 2022, 43(12): 5667-5675.

镁改性硅藻土回收废水氮磷产物对水中Pb²⁺和Zn²⁺的去除

吴盈秋, 夏鹏, 李远, 王学江

同济大学环境科学与工程学院, 污染控制与资源化研究重点实验室, 上海 200092

收稿日期: 2022-03-07; 修订日期: 2022-04-15

基金项目: 国家重点研发计划项目（2021YFC3201302-03）

作者简介: 吴盈秋(1999~), 女, 硕士研究生, 主要研究方向为污水处理及资源化利用, E-mail: yqwu0815@163.com

通信作者: 王学江, E-mail: wangxj@tongji.edu.cn

摘要: 通过使用镁改性硅藻土回收废水中的氮磷营养素，优化制备了一种复合材料（D-MAP），并将其用于废水中重金属Pb²⁺和Zn²⁺的去除.研究探讨了材料投加量、反应时间、反应温度和溶液初始pH等因素对Pb²⁺和Zn²⁺在D-MAP上吸附的影响.D-MAP吸附去除Pb²⁺和Zn²⁺的最优条件为：D-MAP投加量分别为0.25 g·L^-1和0.30 g·L^-1，Pb²⁺和Zn²⁺初始浓度分别为300 mg·L^-1和60 mg·L^-1，溶液初始pH为5.0.在此条件下，其对Pb²⁺和Zn²⁺去除率分别可达78.67%和89.66%.动力学和热力学的结果表明，D-MAP对Pb²⁺和Zn²⁺的吸附更符合准二级动力学模型；其吸附等温线可用Langmuir模型描述，吸附是自发吸热的过程.Langmuir等温拟合结果指出，D-MAP对Pb²⁺和Zn²⁺的最大吸附容量分别为901.0 mg·g^-1和206.2 mg·g^-1.使用SEM/EDS、XRD和FT-IR等手段对吸附Pb²⁺和Zn²⁺前后的吸附剂进行表征，结果表明，D-MAP是一种鸟粪石-硅藻土复合材料，可通过与Pb²⁺和Zn²⁺生成Pb₁₀（PO₄）₆（OH）₂和Zn₃（PO₄）₂·2H₂ O去除废水中Pb²⁺和Zn²⁺.D-MAP对Pb²⁺和Zn²⁺的去除效果随着pH的增加而增加，且最终产物形态随pH不同产生变化.

关键词: 硅藻土鸟粪石氮磷回收重金属吸附

Removal of Pb(Ⅱ) and Zn(Ⅱ) from Wastewater via Magnesium-Modified Diatomite Product Recovering Nitrogen and Phosphorus

WU Ying-qiu , XIA Peng , LI Yuan , WANG Xue-jiang

State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China

Abstract: By using magnesium-modified diatomite to recover nitrogen and phosphorus nutrients from wastewater, a composite material (D-MAP) was applied to remove the heavy metal ions Pb²⁺and Zn²⁺ in wastewater. The effects of material dosage, reaction time, reaction temperature, and initial pH of the solution on the adsorption of Pb²⁺ and Zn²⁺ on D-MAP were studied. The optimum conditions were as follows: the dosage of D-MAP was 0.25 g·L^-1 and 0.30 g·L^-1, the initial concentrations of Pb²⁺ and Zn²⁺ were 300 mg·L^-1 and 60 mg·L^-1, and the initial pH of the solution was 5.0. Under these conditions, the removal rates of Pb²⁺ and Zn²⁺ reached 78.67% and 89.66%. The results of kinetics and thermodynamics showed that the adsorption of Pb²⁺ and Zn²⁺ by D-MAP was more consistent with the quasi-second-order kinetic model, and the adsorption isotherm was described by the Langmuir model. The adsorption was a spontaneous endothermic process, and the maximum adsorption capacities for Pb²⁺ and Zn²⁺ were 901.0 mg·g^-1 and 206.2 mg·g^-1, respectively. The adsorbents before and after adsorption of Pb²⁺ and Zn²⁺ were characterized by SEM/EDS, XRD, and FT-IR. The results showed that D-MAP was a struvite-diatomite composite, which could be combined with Pb²⁺ and Zn²⁺ to form Pb₁₀(PO₄)₆(OH)₂ and Zn₃(PO₄)₂·2H₂O. The removal efficiency of Pb²⁺ and Zn²⁺ by D-MAP increased with the increase in pH, and the morphology of the final product changed with differing pH.

Key words: diatomite struvite nitrogen and phosphorus recovery heavy metal adsorption

铅(Pb)和锌(Zn)是水土环境中的常见重金属污染物, 废水中的Pb²⁺和Zn²⁺主要来源于金属矿开采、冶炼加工和机械制造等行业^{[1, 2]}.含铅锌废水外排会造成水资源浪费及严重环境污染^[3], 废水中的Pb²⁺和Zn²⁺毒性高且难以降解, 易通过生物富集等方式威胁人类的健康^[4], 因此, 有必要采取绿色经济的技术手段去除废水中Pb²⁺和Zn²⁺等重金属.废水中重金属处理常用技术主要包括离子交换法^{[5, 6]}、化学沉淀法^{[7, 8]}、吸附法^{[9, 10, 11]}、电化学^{[12, 13]}和膜分离方法等^{[14, 15]}.其中, 吸附法因可行性好、适应性广而成为处理重金属废水最常用的方法之一^[16].目前, 已有多项研究工作致力于开发低成本吸附剂, 如黏土矿物^[17]、磷酸盐材料^{[18, 19]}、生物炭^[20]和沸石^[21]等, 以用于废水重金属处理.

含磷材料如磷酸盐和羟基磷灰石等, 在水环境中可产生大量的磷酸根离子, 其产生的磷酸根可与大多数重金属离子形成高化学稳定性的沉淀物^{[22, 23]}.因此, 含磷材料在废水重金属钝化去除方面极具潜力.然而, 磷作为一种不可再生和有限的资源, 在全球范围内正日益枯竭^[24].利用鸟粪石结晶法从污水中同步回收氮磷是环境修复领域研究热点, 兼具经济和环保效益^{[25, 26]}.有研究使用载镁炭质黏土回收废水中的氮磷^[27], 并将回收产物用于废水中Cu²⁺的去除, 其结果表明, 鸟粪石炭质黏土复合材料对Cu²⁺吸附量可达182.8 mg·g^-1, 去除率可达93.04%.

硅藻土是一种硅质生物沉积岩, 本身具有一定吸附能力^[28], 同时可以作为污水中生成鸟粪石的载体便于后续分离回收^[29], 因此, 在本课题组使用氧化镁改性硅藻土回收模拟废水中氮磷的研究基础上^[30], 本文以所得的氮磷回收产物鸟粪石-硅藻土复合材料(D-MAP)为吸附剂, 考察其在不同条件下对废水中Pb²⁺和Zn²⁺的去除能力和相关去除机制, 以期为废水氮磷资源化及重金属废水污染治理提供有效途径.

1 材料与方法 1.1 材料制备

将硅藻土按照固液比为1:20加入到MgCl₂溶液中, 混合搅拌30 min, 按照OH^-/Mg²⁺为2:0缓慢滴加NaOH溶液至硅藻土混合溶液中, 将混合溶液在振荡培养箱中以150 r·min^-1的转速反应陈化24 h, 将过滤后的沉淀清洗和烘干后, 置于马弗炉中, 在450℃下煅烧2 h, 即得镁改性硅藻土D-MgO.将适量KH₂PO₄·6H₂O和NH₄Cl溶解于水中制备氮磷浓度均为60 mg·L^-1的混合溶液, 在1 L模拟氮磷废水中加入0.30 g的D-MgO, 并将混合物置于振荡培养箱中, 在25℃和150 r·min^-1的条件下反应12 h后, 将沉淀过滤和洗涤后, 在80℃下烘干, 即得D-MAP材料.

实验所用药品均采购自国药集团, 分析纯.原材料硅藻土由天津某化工公司提供.实验用水皆为超纯水.

1.2 实验方法

将一定量的Pb(NO₃)₂和Zn(NO₃)₂·6H₂O分别溶解于超纯水中制备实验所用的模拟Pb²⁺和Zn²⁺废水, 使用0.01 mol·L^-1的HNO₃和0.01 mol·L^-1的NaOH调节溶液pH值.反应前后溶液经0.22 μm滤膜过滤后, 采用ICP-Agilent 720ES光谱仪测定溶液中Pb²⁺和Zn²⁺浓度.采用GB 11893-89钼酸铵分光光度法测定溶解性磷酸盐浓度(P_T).

1.2.1 材料投加量优化

配制一系列50 mL Pb²⁺(300 mg·L^-1)和Zn²⁺(60 mg·L^-1)的溶液, 分别投加入0.05、0.10、0.15、0.20、0.25、0.30、0.35、0.40、0.45和0.50 g·L^-1的D-MAP材料, 调节溶液初始pH为5.0, 置于恒温振荡培养箱中, 在25℃和150 r·min^-1条件下反应12 h后, 取样测定Pb²⁺、Zn²⁺和剩余磷的浓度.

1.2.2 吸附动力学

向50 mL Pb²⁺初始浓度为300 mg·L^-1的溶液中投加0.25 g·L^-1的D-MAP, 向50 mL Zn²⁺初始浓度为60 mg·L^-1的溶液中投加0.30 g·L^-1的D-MAP, 调节溶液初始pH为5.0, 将混合液置于恒温振荡培养箱中, 在25℃和150 r·min^-1条件下反应, 每隔一定时间取样测定Pb²⁺和Zn²⁺浓度, 并计算吸附量.

1.2.3 吸附热力学

向50 mL Pb²⁺初始浓度为300 mg·L^-1的溶液中投加0.25 g·L^-1的D-MAP, 向50 mL Zn²⁺初始浓度为60 mg·L^-1的溶液中投加0.30 g·L^-1的D-MAP, 调节溶液初始pH为5.0, 将混合液置于恒温振荡培养箱中, 在不同温度(288、298和308 K), 150 r·min^-1条件下反应, 取样测定Pb²⁺和Zn²⁺浓度, 并计算吸附量.

1.2.4 溶液初始pH的影响

向一系列50 mL Pb²⁺初始浓度为300 mg·L^-1的溶液中投加0.25 g·L^-1的D-MAP, 向50 mL Zn²⁺初始浓度为60 mg·L^-1的溶液中投加0.30 g·L^-1的D-MAP, 调节溶液初始pH分别为3.0、4.0、5.0、6.0、7.0, 将混合液置于恒温振荡培养箱中, 在25℃、150 r·min^-1条件下反应, 取样测定Pb²⁺和Zn²⁺浓度, 并计算吸附量.

1.3 材料表征

采用Zeiss Ultra 55场发射扫描电子显微镜(SEM)观测材料表面的微观形貌; 采用X射线能谱仪(EDS)分析材料表面局部的化学组成, 采用Bruker D8 advance型X射线衍射仪(XRD)对材料进行物相分析, 采用Nicolet Nexus 470傅里叶红外光谱仪(FT-IR)对材料进行分子结构分析.

2 结果与讨论 2.1 D-MAP的表征

图 1 (a)和1(b)的结果指出, 硅藻土原土具有蜂窝状结构, 且表面光滑, 经MgO改性后, 材料表面微孔结构被纳米氧化镁覆盖.图 1 (c)结果指出, 回收氮磷后, D-MgO表面负载的MgO颗粒消失, 材料中可观察到棒状结晶附着在硅藻土表面.对棒状结晶进行EDS扫描, 结果指出, 其组成元素主要为Mg、N和P元素.

(a) 硅藻土; (b) D-MgO; (c) D-MAP 图 1 硅藻土、D-MgO和D-MAP的SEM图像 Fig. 1 SEM images of diatomite, D-MgO, and D-MAP

FT-IR表征结果如图 2所示.由图 2 (a)可知, 回收氮磷后, 材料中对应于MgO的衍射峰消失, 并在2θ为15.85°、20.91°、21.50°和31.97°处观察到对应于MgNH₄PO₄(JCPDS 07-0239) (020)、(111)、(021) 和(040) 晶面的特征衍射峰, 结合EDS的结果可确定, D-MAP中棒状结晶主要成分为鸟粪石.由图 2 (b)可知, D-MAP的FT-IR图谱中, 在波数为3 825 cm^-1和3 261 cm^-1处的弱吸收峰代表O—H的伸缩振动(≡Si—OH和≡Fe—OH)^[31].与D-MgO相比较, D-MAP位于500 cm^-1的MgO吸收峰减弱, 在波数为568 cm^-1和1 004 cm^-1处观察到了对应于PO₄^3-的吸收峰, 在波数为1 444 cm^-1和1 656 cm^-1处观察到了对应于NH₄⁺的吸收峰^[32]. 上述结果指出, 在以D-MgO回收废水中氮磷组分的过程中, 氮磷以鸟粪石结晶的形式附着在硅藻土基质上, 所得D-MAP是一种硅藻土和鸟粪石的复合材料.

图 2 D-MgO和D-MAP的XRD和FT-IR Fig. 2 XRD patterns and FT-IR spectrum of D-MgO and D-MAP

2.2 材料投加量优化

吸附剂的投加量会影响其吸附效果^[33].图 3反映了不同D-MAP投加量下, 溶液中Pb²⁺和Zn²⁺去除率和溶液中剩余磷P_T浓度的变化.由图 3 (a)可知, 在投加量小于0.25 g·L^-1时, 溶液中Pb²⁺的去除率随投加量增加而快速增加, 去除率迅速提高到78.67%, 当投加量高于0.25 g·L^-1时, 材料对Pb²⁺的去除率变化趋势放缓, 同时, 溶液中的P_T浓度由初始的较低状态开始陡增, 这可能是由于D-MAP投加过量, 材料在溶液中所释放的磷酸根与铅沉淀出现过剩.同样, 图 3 (b)的结果也指出, 溶液中Zn²⁺的去除率也随着投加量的增加而快速上升, 投加量达到0.30 g·L^-1时, 去除率为89.66%.当投加量超过0.30 g·L^-1后达到平衡, 溶液中P_T浓度也开始上升.参考重金属离子的去除率和溶液中的磷浓度, D-MAP去除溶液中Pb²⁺最佳投加量选取0.25 g·L^-1, 去除溶液中Zn²⁺时则选取0.30 g·L^-1.

(a) 投加量对D-MAP去除Pb²⁺的影响; (b)投加量对D-MAP去除Zn²⁺的影响图 3 材料投加量对D-MAP去除Pb²⁺和Zn²⁺的影响 Fig. 3 Effect of material dosage on the removal of Pb²⁺ and Zn²⁺ by D-MAP

2.3 吸附动力学

图 4给出了D-MAP对Pb²⁺和Zn²⁺吸附动力学曲线, 使用准一级动力学和准二级动力学模型^{[34, 35]}对实验数据进行拟合分析.从中可知, D-MAP对Pb²⁺和Zn²⁺的吸附量分别在120 min和60 min内迅速增加, 之后逐渐趋于平衡, 反应时间延长并不能显著提升吸附容量.D-MAP对Pb²⁺和Zn²⁺的平衡吸附量则分别达到835.78 mg·g^-1和174.72 mg·g^-1.

图 4 反应时间对D-MAP去除Pb²⁺和Zn²⁺的影响 Fig. 4 Effect of reaction time on the removal of Pb²⁺ and Zn²⁺ by D-MAP

2种动力学模型的参数如表 1所示.D-MAP吸附Pb²⁺和Zn²⁺的准二级动力学模型的相关系数R², 要显著高于准一级动力学拟合的相关系数, 且拟合所得的q_e更接近于实际值.因此, 准二级动力学模型可以更好地解释D-MAP对溶液中Pb²⁺和Zn²⁺的吸附性质, 这表明在吸附过程中可能伴随着较强的化学作用力^[36].

表 1 D-MAP吸附Pb²⁺和Zn²⁺的准一级和准二级动力学模型拟合参数 Table 1 Pseudo-first-order and pseudo-second order kinetic model fitting parameters for Pb²⁺and Zn²⁺ adsorption by D-MAP

2.4 吸附热力学

图 5给出了不同反应温度对D-MAP去除Pb²⁺和Zn²⁺的影响结果, 由图 5 (a)可知, D-MAP对Pb²⁺的吸附量随着溶液中Pb²⁺平衡浓度的增加而增加, 在Pb²⁺平衡浓度较低时, D-MAP对Pb²⁺的吸附量快速上升, 当Pb²⁺平衡浓度达到198.5 mg·L^-1时, D-MAP对Pb²⁺的吸附趋于饱和.D-MAP对溶液中Zn²⁺的吸附也呈现出类似趋势[图 5 (b)].

图 5 反应温度对D-MAP去除Pb²⁺和Zn²⁺的影响 Fig. 5 Effect of reaction temperature on the removal of Pb²⁺ and Zn²⁺ by D-MAP

采用Langmuir和Freundlich两种等温吸附模型^{[37, 38]}对数据进行拟合, 拟合结果如表 2和图 6所示.在T=308 K时, D-MAP对Pb²⁺和Zn²⁺的吸附量最高, 当温度下降时, 其对Pb²⁺和Zn²⁺的吸附量也随之下降.上述结果说明, D-MAP对Pb²⁺和Zn²⁺的吸附过程是吸热反应, 高温度对二者在D-MAP上的吸附有促进作用, 在308 K下, D-MAP对二者的最大吸附量分别为901.0 mg·g^-1和206.2 mg·g^-1.Langmuir模型对D-MAP吸附Pb²⁺和Zn²⁺数据拟合的相关系数R²均大于0.99, 结果指出, Langmuir模型可以更好地描述Pb²⁺和Zn²⁺在D-MAP上的等温吸附, 其吸附机制更倾向于单层化学型吸附.

表 2 D-MAP吸附Pb²⁺和Zn²⁺的Langmuir和Freundlich热力学模型的参数 Table 2 Langmuir and Freundlich isotherm parameters for Pb²⁺ and Zn²⁺ adsorption by D-MAP

(a) 和(b) 为Langmuir模型的线性拟合; (c) 和(d)为Freundlich模型的线性拟合图 6 Pb²⁺和Zn²⁺在D-MAP上的等温吸附模型拟合结果 Fig. 6 Fitting results of adsorption isotherm of Pb²⁺ and Zn²⁺on D-MAP

使用范特霍夫方程对不同温度下, Pb²⁺和Zn²⁺在D-MAP材料上的吸附等温线^[39]进行拟合, 并计算相应吸附的热力学参数^[40], 结果如表 3所示.从中可知, Pb²⁺和Zn²⁺在D-MAP材料上吸附过程的ΔG^θ都为负值, 说明在实验条件下, Pb²⁺和Zn²⁺的吸附过程都是自发的.此外, Pb²⁺和Zn²⁺在D-MAP上吸附的ΔH^θ的值分别为2.62 kJ·mol^-1和8.81 kJ·mol^-1, 这进一步证明了D-MAP对Pb²⁺和Zn²⁺的吸附都是吸热过程.随着反应温度的升高, ΔG^θ减小, 这表明高温对吸附过程更有利.Pb²⁺和Zn²⁺吸附的ΔS^θ值都为正值, 表明吸附过程固/液界面无序性增强^[41].

表 3 D-MAP吸附Pb²⁺和Zn²⁺的热力学参数 Table 3 Thermodynamic parameters for Pb²⁺and Zn²⁺ adsorption by D-MAP

2.5 溶液初始pH的影响

溶液pH是吸附的重要影响因素, 溶液pH不仅会影响吸附质在溶液中的赋存形态, 还会影响吸附剂在溶液中的性质, 从而影响到吸附剂对溶液中重金属的去除效果^[42].图 7给出了不同初始pH对D-MAP去除Pb²⁺和Zn²⁺的影响, 当初始pH在3.0~7.0之间时, D-MAP可以有效去除Pb²⁺和Zn²⁺, 且随着溶液pH的升高, D-MAP对溶液中Pb²⁺和Zn²⁺的吸附能力随之提升, 原因可能是在该初始pH范围下, D-MAP水解释放出来的磷酸盐在溶液中以H₂PO₄^-和HPO₄^2-的形式存在^[43], 较易和Pb²⁺和Zn²⁺发生络合反应形成沉淀; 此外, 随pH升高, 溶液中H⁺的浓度降低, 这可减弱H⁺与Pb²⁺或Zn²⁺对D-MAP表面带有负电荷的吸附位点的竞争^[44].Pb²⁺和Zn²⁺在D-MAP上的吸附过程可能发生下述反应：

图 7 初始pH对D-MAP去除溶液中Pb²⁺和Zn²⁺的影响 Fig. 7 Effect of initial pH on the removal of Pb²⁺ and Zn²⁺ by D-MAP

(1)

(2)

(3)

(4)

对不同初始pH(3、5和7)条件下, D-MAP吸附Pb²⁺和Zn²⁺后的回收产物进行XRD和SEM表征分析, 以探讨D-MAP对溶液中Pb²⁺和Zn²⁺的去除机制.图 8给出了Pb²⁺溶液在不同初始pH条件下回收产物的XRD图, 在初始pH为3.0时, 回收产物中除了有铅羟基磷灰石Pb₁₀(PO₄)₆(OH)₂外, 还有部分PbHPO₄生成, 而在相对较高的pH下, 回收产物中主要成分为Pb₁₀(PO₄)₆(OH)₂, 且其特征峰更尖锐, 强度更大, 结晶度更高.Pb₁₀(PO₄)₆(OH)₂在水溶液中溶解度极低, 使Pb²⁺转化为Pb₁₀(PO₄)₆(OH)₂可有效钝化去除废水中的铅^[45].图 9给出了相应回收产物的SEM分析, 从中可知, 与Pb²⁺反应后, D-MAP中棒状鸟粪石结晶消失, 出现了针状的结晶体, 硅藻土作为晶种起富集结晶体的作用.此外, 随着溶液pH的上升, 硅藻土表面磷酸铅化合物从细小颗粒状结晶逐渐转变为细长的针状, 最后变为颗粒状, 说明溶液初始pH不仅影响D-MAP对水溶液中Pb²⁺的去除性能, 也显著影响Pb²⁺最终产物的形态.

图 8 Pb²⁺溶液在不同初始pH条件下回收产物的XRD图谱 Fig. 8 XRD patterns of recycling products of a Pb²⁺ solution under different initial pH conditions

(a) pH=3; (b) pH=5; (b) pH=7 图 9 Pb²⁺溶液在不同初始pH条件下回收产物的SEM图像 Fig. 9 SEM images of recycling products of a Pb²⁺solution under different initial pH conditions

图 10给出了Zn²⁺溶液在不同初始pH条件下回收产物的XRD图谱, 在初始pH为3.0时, D-MAP对Zn²⁺的吸附效果较差, 回收产物中并没有检测出磷酸锌Zn₃(PO₄)₂·2H₂O特征峰, 而在相对较高的pH下, 回收产物中逐渐出现Zn₃(PO₄)₂·2H₂O, 且强度也在变大.图 11给出了相应回收产物的SEM分析, 从中可知, D-MAP与Zn²⁺反应后, 随着溶液pH上升, 硅藻土表面磷酸锌化合物从稀疏的颗粒结晶逐渐转变为絮状生长.

图 10 Zn²⁺溶液在不同初始pH条件下回收产物的XRD图谱 Fig. 10 XRD patterns of recycling products of a Zn²⁺ solution under different initial pH conditions

(a) pH=3; (b) pH=5; (b) pH=7 图 11 Zn²⁺溶液在不同初始pH条件下回收产物的SEM图像 Fig. 11 SEM images of recycling products of a Zn²⁺ solution under different initial pH conditions

综上可得, D-MAP材料与Pb²⁺和Zn²⁺的反应产物中分别观察到Pb₁₀(PO₄)₆(OH)₂和Zn₃(PO₄)₂·2H₂O, 说明在向Pb²⁺和Zn²⁺污染的废水中投加鸟粪石-硅藻土材料D-MAP后, 溶液中发生了材料溶出的磷酸根离子与Pb²⁺和Zn²⁺的化学沉淀反应.

3 结论

(1) 溶液中Pb²⁺和Zn²⁺的初始浓度分别为300 mg·L^-1和60 mg·L^-1, 条件实验的结果指出, D-MAP对Pb²⁺和Zn²⁺去除的最佳投加量分别为0.25 g·L^-1和0.30 g·L^-1, 在此投加量下, 对二者去除率可分别达到78.67%和89.66%.

(2) 吸附动力学结果指出, D-MAP对Pb²⁺和Zn²⁺的吸附分别在120 min和60 min后达到平衡, 吸附过程符合准二级动力学模型; 吸附热力学结果指出, D-MAP对Pb²⁺和Zn²⁺的吸附更符合Langmuir模型.

(3) D-MAP对Pb²⁺和Zn²⁺的去除率随溶液初始pH值呈正相关.D-MAP吸附Pb²⁺和Zn²⁺后回收产物的XRD和SEM表征结果指出, D-MAP主要通过生成Pb₁₀(PO₄)₆(OH)₂和Zn₃(PO₄)₂·2H₂O沉淀的方式, 去除废水中的Pb²⁺和Zn²⁺.

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环境科学 2022, Vol. 43 Issue (12): 5667-5675	PDF