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目前,矿井废水的利用率不断提高,处置后的矿井废水多用于工业用水等,只有少部分能作为居民饮用水回用,其中最主要的制约因素之一就是氟离子含量超标[1]。氟是一种持久性和不可降解的有毒物质,饮用含有过量氟的饮用水,会对人体健康造成威胁[1]。长期饮用高氟水而导致的氟斑牙、氟骨症等蓄积性氟中毒是全球影响最广的地方病之一,氟过量摄入对儿童智商也有明显影响[2-3]。然而,最近的研究[1]表明,人体软组织也会受到氟离子影响,这种类型的氟中毒被称为非骨骼性氟中毒。已经发布的地下水质量标准(GB/T 14848-2017)和污水排放标准(GB 8978-1996)中均明确规定了氟离子和氟化物的排放质量浓度限值,即1.0 mg·L−1和10 mg·L−1。同时,地下水中也发现了各种不同浓度的金属和非金属离子,如铁离子、镁离子、钙离子、钠离子、氯离子、碳酸根离子等,相比于其他离子,氟离子过量被认为具有更大危害[4]。此外,氟甚至可以引起神经系统[5]、内分泌腺[6]、生殖系统、肾脏、肝脏[7]等器官的代谢、结构和功能损伤。氟中毒的数量惊人[1, 8],全球约有25个国家受到氟中毒的影响。氟化物污染在世界不同地区的地下水中被广泛报道,其中包括非洲、拉丁美洲和亚洲的潮湿热带地区[9]。鉴于氟化物对人体健康的毒性影响,迫切需要找到一种有效且稳健的技术来去除水环境中过量的氟化物[10]。
去除矿井废水中氟离子的主要方法有混凝沉淀法[11-12],离子交换法[13]、吸附法[14]、膜分离法[15]等。混凝沉淀法因具有效率高、操作简单、投资少等优点而受到普遍认可。混凝沉淀法是向水中投放具有凝聚能力的物质,形成大量胶体,通过沉淀将氟离子从水中去除的过程[16]。常规混凝剂有硫酸铝[17]、氯化铝[18]、硫酸亚铁[19]、硫酸钙[20]等。相对于其他混凝剂,聚合氯化铝(polyaluminum chloride,PAC)具有水解速度快、吸附能力强、巩花大、质密、沉淀快等优点而备受关注[21]。
响应曲面法(response surface methodology,RSM)是一种能够优化工艺参数、减少实验次数以及评估各种影响因素水平及交互作用的有效方法[22-26]。与传统的单因素法和正交实验法相比,RSM优势是,在实验条件优化过程中,可以连续地对实验各个水平进行分析,通过建立影响因素和响应值之间的多元二次回归方程来拟合二者之间的函数关系,克服了单因素法和正交实验法无法解释各因素之间的相互作用,以及无法给出因素和响应值之间的明确回归模型的缺陷[23-24]。
本研究依据RSM中的Box-Behnken Design(BBD)实验设计原理,对铝氟摩尔比(r)、pH和凝聚时间3个影响因素对氟离子的水平影响及其之间的交互作用进行探究,明确去除氟离子的最佳条件参数,旨在为含氟矿井水的处理提供新的技术方案和科学依据。
基于响应曲面法的聚合氯化铝对矿井废水中氟离子混凝去除工艺优化
Optimization of coagulation removal of fluoride ions from mine wastewater by polyaluminum chloride based on response surface methodology
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摘要: 为有效去除矿井废水中氟离子,利用聚合氯化铝(PAC)对某矿井含氟废水进行混凝效果研究,设计单因素实验,研究了铝氟摩尔比(r)、pH和凝聚时间等因素对PAC混凝去除氟离子的影响,依据响应曲面法的Box-Behnken Design(BBD)实验设计原理,探究了r、pH和凝聚时间对混凝效果的影响,并优化工艺参数。结果表明:各因素对混凝效果的影响顺序为r > pH > 凝聚时间;在r=19.04、pH=6.5、凝聚时间为2.9 min的最佳条件下,氟离子的去除率为56.4%,与预测值(56.46%)基本吻合;去除氟离子的机理包括PAC对氟离子絮凝沉淀、离子交换和络合沉降等;pH影响PAC在溶液中的存在状态,凝聚时间则影响矾花在溶液中形成的速度以及密集程度,进而影响混凝沉淀效果。由此可以看出,BBD优化模型预测与实际处理效果基本一致,铝氟摩尔比和pH是去除氟离子的主要控制因素。本研究使用的实验方法具有处理工艺简单、效果稳定、成本低等优点,可为实际矿井废水中氟离子的去除提供参考。
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关键词:
- 聚合氯化铝(PAC) /
- 混凝 /
- 矿井废水 /
- 氟离子
Abstract: In order to effectively remove fluoride ions from mine wastewater, the coagulation effect of polymerized aluminum chloride (PAC) on a mine fluoride wastewater was studied, a single-factor experiment was designed to investigate the effects of aluminum-fluoride molar ratio (r), pH and coagulation time on the removal of fluoride ions by PAC coagulation. Based on the Box-Behnken Design (BBD) experimental design principle of response surface method, the effects of r, pH and coagulation time on the coagulation effect were investigated, and the process parameters were optimized. The results showed that the coagulation effect was orderly influenced by r>pH>coagulation time. Under the optimal conditions of r=19.04, pH=6.5 and coagulation time of 2.9 min, the removal rate of fluoride ions was 56.4%, which was consistent with the predicted value (56.46%). The mechanism of fluoride ions removal included flocculation and precipitation of fluoride ions by PAC, ion exchange and complexation precipitation, etc.. pH affected the speciation of PAC in the solution, and the coagulation time affected the formation rate and compactness of alum flocs in the solution, which further affected the coagulation and precipitation effect. It can be seen that the prediction of BBD optimization model was basically consistent with the actual treatment effect, and the molar ratio of aluminum to fluorine and pH were the main controlling factors for fluoride ions removal. The experimental method used in this study has the advantages of simple treatment process, stable effect and low cost, which can provide a reference for the removal of fluoride ions in actual mine wastewater.-
Key words:
- polymeric aluminum chloride(PAC) /
- coagulation /
- mine wastewater /
- fluoride
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表 1 响应面实验设计
Table 1. Response surface test design
水平 因素 (A)铝氟摩尔比 (B)pH (C)凝聚时间/min −1 10 6 1 0 15 6.5 2 +1 20 7 3 表 2 响应面实验设计和结果
Table 2. Response surface test design and results
实验号 (A)铝氟摩尔比 (B)pH (C)凝聚时间 去除率/% 1 15 6.0 3 41.10 2 20 7.0 2 41.10 3 20 6.5 3 56.44 4 15 7.0 3 38.95 5 15 6.5 2 49.70 6 15 7.0 1 34.36 7 10 7.0 2 17.18 8 20 6.0 2 47.24 9 15 6.0 1 38.95 9
1015
206.0
6.51
138.95
54.6011 15 6.5 2 47.24 12 10 6.5 3 34.36 13 15 6.5 2 49.70 14 10 6.0 2 23.31 15 10 6.5 1 31.90 表 3 回归方程的方差分析与回归模型的可信度分析表
Table 3. Analysis of variance of regression equations and credibility of regression model
方差来源 平方和 自由度 均方 F值 P值 模型 1 697.33 9 188.59 96.42 <0.000 1 (A)铝氟摩尔比 1 072.54 1 1 072.54 548.37 <0.000 1 (B)pH 45.17 1 45.17 23.10 0.004 9 (C)凝聚时间 15.24 1 15.24 7.79 0.038 4 AB 0.000 0 1 0.000 0 0.000 0 0.997 3 AC 0.096 1 1 0.096 1 0.049 1 0.833 3 BC 1.49 1 1.49 0.761 0 0.422 9 A2 105.44 1 105.44 53.91 0.000 7 B2 473.87 1 473.87 242.28 <0.000 1 C2 2.30 1 2.30 1.17 0.328 0 残差 9.78 5 1.96 失拟项 5.74 3 1.91 0.949 3 0.549 7 误差 4.03 2 2.02 总离差 1 707.11 14 表 4 二次响应面回归模型预测值验证
Table 4. Verification of the predicted value of the quadratic response surface regression model
铝氟摩尔比(r) pH 凝聚时间/min 实际去除率/% 19.04 6.50 2.90 56.44 19.04 6.50 2.90 56.44 19.04 6.50 2.90 56.44 -
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