巰基聚苯乙烯樹(shù)脂對(duì)FGD系統(tǒng)中Hg2+的脫除性能

付康麗，姚明宇，欽傳光，程廣文，聶劍平（西安熱工研究院有限公司國(guó)家能源清潔高效火力發(fā)電技術(shù)研發(fā)中心，陜西 西安 70054；西北工業(yè)大學(xué)理學(xué)院，陜西 西安 7007）

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巰基聚苯乙烯樹(shù)脂對(duì)FGD系統(tǒng)中Hg2+的脫除性能

付康麗1，姚明宇1，欽傳光2，程廣文1，聶劍平1
（1西安熱工研究院有限公司國(guó)家能源清潔高效火力發(fā)電技術(shù)研發(fā)中心，陜西 西安 710054；2西北工業(yè)大學(xué)理學(xué)院，陜西 西安 710072）

摘要：以氯甲基化聚苯乙烯微球?yàn)樵希?jīng)過(guò)兩步反應(yīng)制得巰基聚苯乙烯樹(shù)脂，用紅外光譜測(cè)試、比表面分析、元素分析及熱重分析表征了該巰基聚苯乙烯樹(shù)脂，測(cè)試了此巰基聚苯乙烯樹(shù)脂對(duì)含Hg2+煙氣、脫硫廢水及脫硫漿液的脫汞性能。分析測(cè)試表明：巰基聚苯乙烯樹(shù)脂熱穩(wěn)定性好，能有效脫除煙氣、脫硫廢水及脫硫漿液中的Hg2+。巰基聚苯乙烯樹(shù)脂對(duì)煙氣中Hg2+的脫除效率大于90%，對(duì)脫硫廢水及脫硫漿液的脫汞率接近100%。將此樹(shù)脂置于脫硫系統(tǒng)內(nèi)，能捕捉脫硫系統(tǒng)內(nèi)的Hg2+，避免Hg2+進(jìn)入脫硫石膏而造成脫硫石膏中汞的再釋放。用6 mol·L?1鹽酸洗脫捕捉了Hg2+的巰基聚苯乙烯樹(shù)脂，再生3次后，巰基聚苯乙烯樹(shù)脂的再生率仍高達(dá)90.2%。

關(guān)鍵詞：煙道氣；煤燃燒；廢水；汞；巰基樹(shù)脂

2015-11-06收到初稿，2015-11-23收到修改稿。

聯(lián)系人：付康麗，欽傳光。第一作者：付康麗（1986—），女，博士后，高級(jí)工程師。

Received date: 2015-11-06.

Foundation item: supported by the China Postdoctoral Science Foundation (2015M570849) and the National Key Technology Research and Development Program of China (2014BAA07B04).

引　言

汞污染問(wèn)題已成為社會(huì)的焦點(diǎn)問(wèn)題之一。煤燃燒是人為汞排放的最主要來(lái)源[1-2]。煙氣中的汞分為3種形態(tài)，即元素汞（Hg0）、氧化汞（Hg2+）和顆粒汞（Hgp）。在這3種形態(tài)中，Hgp能被布袋除塵或靜電除塵有效除去；Hg2+水溶性好[3]，濕法脫硫系統(tǒng)能脫除高達(dá)99%的Hg2+，此法被認(rèn)為是經(jīng)濟(jì)可行的燃煤電廠多污染物控制方法。然而，Hg0易揮發(fā)且不溶于水，不利于Hg0的脫除。許多研究報(bào)道[4-6]集中于將Hg0氧化成Hg2+，再借助濕法脫硫系統(tǒng)將Hg2+脫除。然而，捕集在濕法脫硫系統(tǒng)中的Hg2+與此系統(tǒng)中的還原性粒子（如亞硫酸根離子）反應(yīng)生成Hg0，造成汞的再釋放[7]。對(duì)此，一些研究集中于降低汞的再釋放的影響因素[1-2,8-12]。

目前，幾乎所有關(guān)于避免煙氣中汞的再釋放的研究都集中于盡可能地將Hg2+保留于脫硫系統(tǒng)中[13-17]。脫硫系統(tǒng)捕集的汞最終將流向脫硫廢水和脫硫石膏[18]。脫硫廢水被凈化處理后作為脫硫工藝水使用。脫硫石膏是脫硫系統(tǒng)中產(chǎn)生的唯一產(chǎn)物，廣泛用作墻板的制作原料。此外，脫硫石膏還用作水泥和混凝土的添加劑及填埋料[19-21]。脫硫石膏中汞的濃度高達(dá)656～1919 ng·g?1[22]，在石膏墻板的制作過(guò)程中將會(huì)有12.1%～55%的汞發(fā)生再釋放[23-24]，造成環(huán)境汞污染。在長(zhǎng)期的化學(xué)和物理作用下，脫硫石膏填埋料中的汞會(huì)滲透土壤進(jìn)入地下水，而且目前還未見(jiàn)到關(guān)于脫除石膏中汞的報(bào)道。此外，將添加劑加入石膏中能抑制汞的再釋放，但也會(huì)降低石膏品質(zhì)，不利于石膏的資源化利用。

因此，基于濕法脫硫系統(tǒng)的Hg2+脫除技術(shù)只能暫時(shí)脫除煙氣中的汞。若要從根本上解決汞污染排放問(wèn)題，就必須研發(fā)新的脫汞劑，而且要求該脫汞劑能將Hg2+從濕法脫硫系統(tǒng)中分離出來(lái)。有機(jī)樹(shù)脂材料由于其優(yōu)異的吸附性而越來(lái)越受關(guān)注，已有研究將改性酚醛樹(shù)脂材料用于燃煤煙氣脫硫脫硝處理，并獲得了優(yōu)異的脫硫性能及較好的脫硝性能[25-28]。大孔聚苯乙烯樹(shù)脂常用于重金屬?gòu)U水處理[29-31]。然而還未見(jiàn)到關(guān)于用樹(shù)脂脫除煙氣中Hg2+的報(bào)道。

本工作的研究目的在于脫除煙氣中的Hg2+，防止Hg2+進(jìn)入脫硫石膏和脫硫廢水，以從根本上脫除煙氣中的Hg2+，并解決汞的再釋放問(wèn)題。制備了一種新型可再生巰基聚苯乙烯樹(shù)脂，并用紅外、比表面分析、元素分析及熱重分析對(duì)其進(jìn)行表征；研究了巰基聚苯乙烯樹(shù)脂對(duì)煙氣中和脫硫廢水中Hg2+的脫除性能；最后探討了巰基聚苯乙烯樹(shù)脂的再生性能。

1　實(shí)驗(yàn)材料和方法

1.1材料

氯甲基化聚苯乙烯樹(shù)脂（交聯(lián)度8%）由南開(kāi)化工廠提供，硫脲（分析純）、NaOH（分析純）、無(wú)水乙醇（分析純）、37%濃鹽酸皆由國(guó)藥集團(tuán)化學(xué)試劑有限公司提供。

1.2巰基聚苯乙烯樹(shù)脂的制備及表征

將硫脲和氯甲基化聚苯乙烯樹(shù)脂置于無(wú)水乙醇中回流反應(yīng)5 h得硫脲基聚苯乙烯樹(shù)脂，在氮?dú)獗Ｗo(hù)下用50% NaOH溶液于80℃水解12 h得巰基聚苯乙烯樹(shù)脂粗產(chǎn)物，經(jīng)水洗—稀鹽酸洗—水洗后，再將巰基聚苯乙烯樹(shù)脂置于無(wú)水乙醇中回流萃取8 h，真空干燥得巰基聚苯乙烯樹(shù)脂[32]。具體制備過(guò)程如圖1所示。制備巰基聚苯乙烯樹(shù)脂后，用紅外光譜、比表面積分析、元素分析、熱重分析對(duì)巰基聚苯乙烯樹(shù)脂進(jìn)行化學(xué)表征。

1.3汞濃度分析

使用Ohio Lumex RA-915+型塞曼汞分析儀，根據(jù)安大略法（ASTM D678—2002）測(cè)試汞濃度。

1.4Hg0的氧化

V2O5基催化劑對(duì)Hg0具有良好的氧化性[33-35]。O2和HCl的加入能促進(jìn)SCR催化劑對(duì)Hg0的氧化效率[36-37]。配制含300 mg·m?3HCl和6% O2及一定濃度Hg0的模擬煙氣（N2為平衡氣體），煙氣流速為0.5 L·min?1，此模擬煙氣流經(jīng)裝有粉末狀SCR催化劑的U形管（置于管式爐中，350℃）。

圖1　巰基聚苯乙烯樹(shù)脂的制備反應(yīng)Fig.1　Synthetic route of thiol polystyrene resin

1.5 巰基聚苯乙烯樹(shù)脂對(duì)煙氣中Hg2+的脫除

此組實(shí)驗(yàn)的目的在于測(cè)定巰基聚苯乙烯樹(shù)脂對(duì)煙氣中Hg2+的脫除效率。圖2是Hg0的氧化吸收反應(yīng)系統(tǒng)。具體實(shí)驗(yàn)過(guò)程如下：將1.0 g巰基聚苯乙烯樹(shù)脂和30 g石英砂混合均勻，將此混合物置于裝有濾氣板的U形管中，使含Hg2+煙氣通過(guò)巰基聚苯乙烯樹(shù)脂。煙氣流速為0.5～1.5 L·min?1，測(cè)試溫度為25～80℃，入口煙氣中Hg2+濃度為32.5 μg·m?3。

圖2　Hg0的氧化及Hg2+的吸收反應(yīng)系統(tǒng)Fig.2　Schematic diagram of mercury adsorption

Hg2+脫除效率（ηHg2+）計(jì)算公式如式（1）所示。

1.6 巰基聚苯乙烯樹(shù)脂對(duì)脫硫廢水和脫硫漿液中Hg2+的脫除

脫硫廢水和脫硫漿液均由華能銅川照金電廠和楊柳青電廠提供。分別取150 ml脫硫廢水、脫硫漿液，向其中加入3 g巰基聚苯乙烯樹(shù)脂，將此體系置于30℃下，以150 r·min?1的攪拌速率攪拌30 min，隨后靜置1 h，過(guò)濾出巰基聚苯乙烯樹(shù)脂，測(cè)試初始脫硫廢水及脫硫漿液和處理后脫硫廢水及脫硫漿液中的汞濃度，計(jì)算脫汞效率。

1.7巰基聚苯乙烯樹(shù)脂的再生

用6 mol·L?1鹽酸和去離子水連續(xù)洗滌捕集了Hg2+的巰基聚苯乙烯樹(shù)脂，測(cè)試洗脫液中的汞含量。

2　實(shí)驗(yàn)結(jié)果與討論

2.1巰基聚苯乙烯樹(shù)脂的性質(zhì)

表1給出了各樹(shù)脂的元素分析結(jié)果。如表中所示，相比氯甲基化聚苯乙烯樹(shù)脂，巰基聚苯乙烯樹(shù)脂中的硫含量具有顯著的提升。氯甲基化聚苯乙烯樹(shù)脂的氯含量為18.8%（此數(shù)據(jù)由南開(kāi)化工廠提供），其他組分含量主要是氯含量。巰基聚苯乙烯樹(shù)脂中的其他組分含量顯著降低，這意味著巰基成功取代了氯基。表中的氮含量主要是在巰基聚苯乙烯樹(shù)脂制備過(guò)程中殘余的少量硫脲基所致。

表1　樹(shù)脂的元素分析Table 1　Elemental analysis for resins

用紅外分析進(jìn)一步確定巰基是否成功嫁接在樹(shù)脂上。如圖3所示，2562 cm?1和2507 cm?1處的吸收峰分別歸屬于S H和結(jié)合Hg2+的S H的伸縮振動(dòng)[38]，672、1250和1264 cm?1處的吸收峰歸屬于C Cl的伸縮振動(dòng)[39]。對(duì)比氯甲基化聚苯乙烯樹(shù)脂和巰基聚苯乙烯樹(shù)脂的紅外光譜圖，巰基聚苯乙烯樹(shù)脂中C Cl的吸收峰強(qiáng)度減弱，而且在2562 cm?1處出現(xiàn)了新的吸收峰，這說(shuō)明S H被成功嫁接在樹(shù)脂上。測(cè)試樣品中含有水，故在圖中3200 cm?1以上波數(shù)處出現(xiàn)的寬吸收峰為樣品中的水的吸收峰[40]。

圖3　樹(shù)脂的紅外光譜圖Fig.3　FTIR spectra for resinsa—thiol polystyrene resin; b—thiol polystyrene resin captured Hg2+; c—regenerated thiol polystyrene resin; d—chloromethyl polystyrene resin, respectively

由圖4可知，巰基聚苯乙烯樹(shù)脂在300℃以下耐熱穩(wěn)定性好。在升溫到800℃的過(guò)程中主要發(fā)生了3次明顯的質(zhì)量損失；第1降解階段為100℃左右，這是由于樣品中含的微量水所引起；第2降解階段始于327℃，此階段降解是樹(shù)脂中的巰基的降解；第3降解階段（427℃）為聚苯乙烯樹(shù)脂的碳鏈降解[41]。

圖4　巰基聚苯乙烯樹(shù)脂熱失重曲線Fig.4　TGA curve of thiol polystyrene resin

此外，為了測(cè)定巰基聚苯乙烯樹(shù)脂的吸附性能，測(cè)試了其比表面性。從理論上說(shuō)，樹(shù)脂的比表面積越高，樹(shù)脂的吸附容量越大[42]。從表2可知，SH的引入在一定程度上降低了樹(shù)脂的比表面積、孔徑和孔容。表中的樹(shù)脂都具有比表面積較大、孔容較寬、孔徑較長(zhǎng)的特點(diǎn)，這為樹(shù)脂對(duì)煙氣中Hg2+的吸附做好了準(zhǔn)備。

表2　樹(shù)脂的孔徑表面積分析Table 2　Pore and surface characteristics of resins

2.2各因素對(duì)煙氣脫汞的影響規(guī)律

將制備的巰基聚苯乙烯樹(shù)脂用于煙氣脫汞處理，研究了影響脫汞性能的因素?？疾焯幚頃r(shí)間對(duì)脫汞性能的影響時(shí)，以巰基聚苯乙烯樹(shù)脂作為脫汞吸收劑，其煙氣流速為1.0 L·min?1，處理溫度為40℃。實(shí)驗(yàn)結(jié)果如圖5所示，處理1 h后脫汞效率為95.3%，而且脫汞效率隨處理時(shí)間延長(zhǎng)而降低。分析其原因?yàn)閹€基聚苯乙烯樹(shù)脂對(duì)煙氣中Hg2+的捕獲機(jī)理為軟硬酸堿理論。根據(jù)軟硬酸堿理論，巰基為軟堿，Hg2+為軟酸，軟酸和軟堿極易結(jié)合成絡(luò)合物[43-44]，具體吸附機(jī)理如下[45]

圖5　處理時(shí)間對(duì)Hg2+脫除效率的影響Fig.5　Influence of treatment time on Hg2+removal efficiency

巰基聚苯乙烯樹(shù)脂對(duì)Hg2+的捕集消耗了其中的巰基，故使得脫汞效率隨處理時(shí)間延長(zhǎng)而降低。此外，由圖3可知巰基和Hg2+的結(jié)合不僅削弱了巰基的吸收峰（2562 cm?1），而且產(chǎn)生了巰基和Hg2+結(jié)合物的吸收峰（2506 cm?1），這證實(shí)Hg2+與巰基發(fā)生了化學(xué)吸附。當(dāng)處理時(shí)間大于2 h時(shí)脫汞效率低于87.5%，故處理時(shí)間不宜長(zhǎng)于2 h。

為了測(cè)定處理溫度對(duì)煙氣脫汞效率的影響，以巰基聚苯乙烯樹(shù)脂為脫汞吸收劑，煙氣流速為0.5 L·min?1，處理時(shí)間為1 h。由圖6可知脫汞效率隨處理溫度升高而降低。這意味著巰基聚苯乙烯樹(shù)脂與Hg2+的結(jié)合屬于放熱反應(yīng)，升高溫度不利于其結(jié)合[46-48]。當(dāng)處理溫度不高于60℃時(shí)脫汞效率均能達(dá)80%以上，而濕法脫硫系統(tǒng)的漿液溫度約為50℃[49]，這為該樹(shù)脂應(yīng)用于濕法脫硫系統(tǒng)做好了準(zhǔn)備。巰基聚苯乙烯樹(shù)脂與脫硫漿液混合，當(dāng)煙氣通過(guò)脫硫塔時(shí)巰基樹(shù)脂捕獲煙氣中的Hg2+，形成穩(wěn)定配合物，避免Hg2+進(jìn)入脫硫廢水和脫硫石膏，從根本上解決汞的再釋放問(wèn)題，從而克服了濕法脫硫系統(tǒng)脫汞的弊端。

圖6　處理溫度對(duì)煙氣脫汞效率的影響Fig.6　Influence of treatment temperature on Hg2+removal efficiency

此外，還探討了煙氣流速對(duì)巰基聚苯乙烯樹(shù)脂脫汞效率的影響，實(shí)驗(yàn)結(jié)果如圖7所示。脫汞效率隨煙氣流速增大而降低，當(dāng)煙氣流速不大于1.2 L·min?1時(shí)脫汞效率在90%以上。其原因?yàn)闊煔饬魉俚脑龃蠼档土藷煔夂蛶€基聚苯乙烯樹(shù)脂的接觸時(shí)間。為了獲得高效脫汞，煙氣流速應(yīng)不高于1.2 L·min?1。

圖7　煙氣流速對(duì)脫汞效率的影響Fig.7　Influence of flue gas flow rate on Hg2+removal efficiency

2.3脫硫廢水及脫硫漿液的脫汞處理

脫硫廢水及脫硫漿液中均含一定濃度的Hg2+，汞會(huì)對(duì)環(huán)境和人體健康帶來(lái)危害，因此有必要探討巰基聚苯乙烯樹(shù)脂對(duì)脫硫廢水及脫硫漿液的脫汞效果。本實(shí)驗(yàn)所使用的脫硫廢水和脫硫漿液均取自華能銅川照金電廠和楊柳青電廠，巰基聚苯乙烯樹(shù)脂對(duì)脫硫廢水的脫汞效率均為100%，對(duì)脫硫漿液的脫汞率分別為100%和99.5%。因此，將巰基聚苯乙烯樹(shù)脂置于脫硫系統(tǒng)內(nèi)，不僅能捕集煙氣中的Hg2+，也能捕集從煙氣中進(jìn)入脫硫廢水和脫硫漿液中的Hg2+，進(jìn)而避免Hg2+進(jìn)入脫硫石膏而造成汞的還原再釋放。

2.4巰基聚苯乙烯樹(shù)脂的再生

對(duì)巰基聚苯乙烯樹(shù)脂的再生處理不僅能降低脫汞成本，而且有助于汞資源的集中處理。從2.2節(jié)中討論的吸附機(jī)理反應(yīng)方程式可知，當(dāng)H+濃度較高時(shí)化學(xué)反應(yīng)平衡向左移動(dòng)，吸附于樹(shù)脂上的Hg2+將釋放至溶液中。以下探討了鹽酸洗脫液pH與樹(shù)脂洗脫效果間的關(guān)系。此樹(shù)脂對(duì)Hg2+的飽和吸附量為3.1 mmol·g?1。

圖8　pH對(duì)巰基聚苯乙烯樹(shù)脂吸附Hg2+的影響Fig.8　Hg2+adsorption over thiol polystyrene resins at various initial pH

從圖8可以看出，當(dāng)pH＞4時(shí)此樹(shù)脂對(duì)Hg2+具有強(qiáng)吸附能力，當(dāng)pH＜1時(shí)此樹(shù)脂幾乎不能吸附Hg2+。基于此，常用濃鹽酸再生巰基聚苯乙烯樹(shù)脂[46,50-51]。用6 mol·L?1鹽酸和去離子水交替洗滌巰基聚苯乙烯樹(shù)脂，再生處理3次后，其再生率仍高達(dá)90.2%。用紅外分析、比表面分析及元素分析表征再生后的巰基聚苯乙烯樹(shù)脂，從表1、表2和圖3可以看出再生后的巰基聚苯乙烯樹(shù)脂和原始聚苯乙烯樹(shù)脂基本性質(zhì)幾乎一樣，這也說(shuō)明了巰基樹(shù)脂被成功再生。用再生的巰基聚苯乙烯樹(shù)脂于40℃下處理煙氣1 h，其脫汞效率為95.0%。此外，從巰基聚苯乙烯樹(shù)脂上洗脫下來(lái)的Hg2+進(jìn)入再生處理液中，這便于實(shí)現(xiàn)Hg2+的集中處理，為實(shí)現(xiàn)汞的資源化利用打下基礎(chǔ)。

本研究制備的巰基聚苯乙烯樹(shù)脂為球狀乳白色顆粒，其平均粒徑為1.15 mm。此樹(shù)脂穩(wěn)定性好，不溶于脫硫漿液、水以及6 mol·L?1鹽酸，通過(guò)簡(jiǎn)單過(guò)濾處理即可將樹(shù)脂從脫硫漿液中分離出來(lái)。此外，經(jīng)再生處理后該樹(shù)脂捕獲的Hg2+進(jìn)入鹽酸洗脫液，樹(shù)脂沉于鹽酸洗脫液底部，過(guò)濾即可實(shí)現(xiàn)樹(shù)脂與洗脫液的分離。

3　結(jié)　論

（1）以氯甲基化聚苯乙烯樹(shù)脂為原料制得了巰基聚苯乙烯樹(shù)脂，該樹(shù)脂具有良好的吸附性能。

（2）巰基聚苯乙烯樹(shù)脂能有效吸附煙氣中和脫硫廢水以及脫硫漿液中的Hg2+。巰基與Hg2+的結(jié)合屬于放熱反應(yīng)，升高溫度不利于二者的結(jié)合。當(dāng)處理溫度低于60℃時(shí)，煙氣脫汞率大于80%，而且對(duì)脫硫廢水的脫汞率高達(dá)100%。

（3）此樹(shù)脂與Hg2+間以化學(xué)吸附為主，當(dāng)pH＜1時(shí)此樹(shù)脂對(duì)Hg2+幾乎不具吸附能力，當(dāng)pH＞4時(shí)此樹(shù)脂對(duì)Hg2+具有強(qiáng)吸附能力。

（4）用6 mol·L?1鹽酸再生處理捕集了Hg2+的巰基聚苯乙烯樹(shù)脂，并分別用紅外光譜、比表面分析、元素分析測(cè)試巰基聚苯乙烯樹(shù)脂。測(cè)試結(jié)果均顯示捕集了Hg2+的巰基聚苯乙烯樹(shù)脂被成功再生。再生處理3次后其再生率仍高達(dá)90.2%，這使得巰基聚苯乙烯樹(shù)脂得以重復(fù)利用。

（5）采用巰基聚苯乙烯樹(shù)脂脫汞具有經(jīng)濟(jì)性高和低污染的優(yōu)點(diǎn)，巰基聚苯乙烯樹(shù)脂有望用于實(shí)際燃煤電廠的脫汞處理中。

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Hg2+removal from FGD system by thiol polystyrene resin

FU Kangli1, YAO Mingyu1, QIN Chuanguang2, CHENG Guangwen1, NIE Jianping1
(1National Energy R & D Center of Clean and High-efficiency Fossil-fired Power Generation Technology, Xi’an Thermal Power Research Institute Limited Company, Xi’an 710054, Shaanxi, China;2School of Natural and Applied Sciences, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China)

Abstract:Thiol polystyrene resin was prepared by two-step reaction with chloromethyl polystyrene resin as material, and then it was characterized by Fourier transform infrared spectroscopy, Brunauer-Emmett-teller, elemental and thermogravimetric analyses. The Hg2+removal performance of thiol polystyrene resin was also investigated in simulated flue gas containing Hg2+, desulfurization effluent and desulfurization slurry. It was found that thiol polystyrene resin possessed high thermal stability and could be used as an absorbent for Hg2+removal from flue gas, desulfurization effluent and desulfurization slurry. The thiol polystyrene resin showed Hg2+removal efficiencies above 90%, 100% and 100% in flue gas, desulfurization effluent and desulfurization slurry, respectively. The placation of thiol polystyrene resin in the wet flue gas desulfurization system could capture Hg2+in this system and avoid its entering to desulfurization gypsum, which could bring the mercury reemission. Moreover, thiol polystyrene resin captured Hg2+was regenerated successfully by 6 mol·L?1HCl and its regeneration rate with three times regeneration reached up 90.2%.

Key words:flue gas; coal combustion; waste water; mercury; thiol resin

中圖分類號(hào)：X 701.7

文獻(xiàn)標(biāo)志碼：A

文章編號(hào)：0438—1157（2016）06—2598—07

DOI：10.11949/j.issn.0438-1157.20151675

基金項(xiàng)目：中國(guó)博士后科學(xué)基金項(xiàng)目（2015M570849）；國(guó)家科技支撐計(jì)劃項(xiàng)目（2014BAA07B04）。

Corresponding author:FU Kangli, 406363513@qq.com;QIN Chuanguang, qinchg@nwpu.edu.cn