李永濤 羅 進(jìn) 岳 東
(西南石油大學(xué)化學(xué)化工學(xué)院,四川 成都 610500)
熱活化過硫酸鹽氧化修復(fù)柴油污染土壤
李永濤 羅 進(jìn) 岳 東
(西南石油大學(xué)化學(xué)化工學(xué)院,四川 成都 610500)
采用熱活化過硫酸鹽法,考察了過硫酸鹽濃度、溫度、水土比和初始pH對(duì)柴油污染土壤氧化修復(fù)的影響,并分析了其動(dòng)力學(xué)和熱力學(xué)參數(shù)。結(jié)果表明,當(dāng)Na2S2O8摩爾濃度為0.8mmol/g、溫度為70 ℃、水土比為2.0mL/g、初始pH為11.00時(shí),反應(yīng)72h后的柴油降解率最高,達(dá)到77.85%。動(dòng)力學(xué)和熱力學(xué)分析表明,熱活化過硫酸鹽氧化降解柴油過程為自發(fā)、吸熱、熵增的過程,表觀活化能為-80.73kJ/mol。
硫酸根自由基 柴油 熱活化 過硫酸鹽
隨著石油工業(yè)的迅速發(fā)展,大量的石油污染物進(jìn)入地表水、包氣帶土層,甚至遷移至地下水,嚴(yán)重影響了生態(tài)環(huán)境和農(nóng)業(yè)生產(chǎn)。因此,石油污染土壤亟待修復(fù)。石油污染物主要包括原油及其煉制品(汽油、煤油、柴油等)。物理修復(fù)雖然是石油污染土壤最重要的修復(fù)方法,但污染物并不能完全去除;生物修復(fù)的修復(fù)周期較長(zhǎng)且對(duì)污染物具有選擇性;相比而言,化學(xué)修復(fù)的優(yōu)勢(shì)是對(duì)污染物具有普適性、修復(fù)周期短且能徹底去除污染物[1-3]。
0#柴油,密度為0.84 g/cm3,購自成都市新都區(qū)某加油站;過硫酸鈉(Na2S2O8)、四氯化碳(CCl4)等,均為分析純?cè)噭?;?shí)驗(yàn)用水為去離子水。
FA2004型電子天平;GKC型數(shù)顯智能恒溫水浴鍋;PHS-3E型pH計(jì);OIL-460型紅外分光測(cè)油儀。
供試土壤,取自西南石油大學(xué)周邊(含油量低于檢出限)0~20 cm的表層土壤,去除礫石、動(dòng)植物殘?bào)w后,于室內(nèi)陰涼處自然風(fēng)干,過60目(0.25 mm)篩備用,風(fēng)干后土壤的含水率為1.12%,總有機(jī)質(zhì)為3.25 g/kg,pH為8.52。
按10.0 mL/kg的油土比把柴油與風(fēng)干土壤混合均勻,置于陰涼干燥通風(fēng)處1周[15],測(cè)得含油量為3 120.09 mg/kg。對(duì)過硫酸鹽濃度、溫度、水土比和初始pH進(jìn)行單因素影響實(shí)驗(yàn),反應(yīng)時(shí)間為72 h。
1.3.1 過硫酸鹽濃度的影響實(shí)驗(yàn)
控制柴油污染土壤10 g、水土比2.0 mL/g、溫度50 ℃、初始pH 6.58,考察Na2S2O8摩爾濃度(0.4~1.0 mmol/g)對(duì)柴油的降解率影響。
1.3.2 溫度的影響實(shí)驗(yàn)
控制柴油污染土壤10 g、水土比2.0 mL/g、初始pH 6.58、Na2S2O8摩爾濃度0.8 mmol/g,考察溫度(30~80 ℃)對(duì)柴油的降解率影響。
1.3.3 水土比的影響實(shí)驗(yàn)
控制柴油污染土壤10 g、Na2S2O8摩爾濃度0.8 mmol/g、初始pH 6.58、溫度70 ℃,考察水土比(0.5、1.0、2.0、3.0、4.0 mL/g)對(duì)柴油的降解率影響。
1.3.4 初始pH的影響實(shí)驗(yàn)
控制柴油污染土壤10 g、水土比2.0 mL/g、Na2S2O8摩爾濃度0.8 mmol/g、溫度70 ℃,考察初始pH(3.00、5.00、7.00、9.00、11.00)對(duì)柴油的降解率影響,并考察了初始pH為3.00、7.00、11.00時(shí)的后續(xù)pH變化。
根據(jù)《城市污水處理廠污泥檢測(cè)方法》(CJ/T 221—2005)中的《城市污泥 礦物油的測(cè)定 紅外分光光度法》測(cè)定含油量,用CCl4作萃取劑, 紅外分光測(cè)油儀測(cè)定,檢出限為0.10 mg/kg。
在Na2S2O8摩爾濃度為0.8 mmol/g、水土比為2.0 mL/g、初始pH為6.00的條件下,考察溫度為40、50、60、70 ℃時(shí)的柴油降解動(dòng)力學(xué)過程,采用準(zhǔn)一級(jí)動(dòng)力學(xué)方程進(jìn)行擬合[16-18],得到表觀反應(yīng)速率常數(shù)(k,s-1)。
熱力學(xué)參數(shù)標(biāo)準(zhǔn)吉布斯自由能變(ΔGθ,J/mol)、標(biāo)準(zhǔn)焓變(ΔHθ,J/mol)和標(biāo)準(zhǔn)熵變(ΔSθ,J/(mol·K))根據(jù)式(1)和式(2)計(jì)算。
ΔGθ=-RTlnk
(1)
(2)
式中:R為理想氣體常數(shù),J/(mol·K),R=8.314 J/(mol·K);T為熱力學(xué)溫度,K。
圖1 Na2S2O8摩爾濃度對(duì)柴油降解率的影響Fig.1 Effect of Na2S2O8 molar concentration on the degradation efficiency of diesel oil
圖2 溫度對(duì)柴油降解率的影響Fig.2 Effect of temperature on the degradation efficiency of diesel oil
圖3 水土比對(duì)柴油降解率的影響Fig.3 Effect of water-soil ratio on the degradation efficiency of diesel oil
由圖4可見,在偏堿性條件和偏酸性條件都有較高的柴油降解率得到,但初始pH為11.00時(shí)柴油降解率相對(duì)最高,為77.85%。進(jìn)一步考察初始pH分別為3.00、7.00、11.00條件下的后續(xù)pH變化,結(jié)果如圖5所示。在3種初始pH條件下進(jìn)行反應(yīng),72 h后pH均降至1.50左右,可能初始pH對(duì)柴油降解率的影響并不是很大。
動(dòng)力學(xué)和熱力學(xué)參數(shù)計(jì)算結(jié)果如表1所示。由表1可知,熱活化過硫酸鹽氧化降解柴油過程的標(biāo)準(zhǔn)吉布斯自由能變均為負(fù)值,表明該過程可自發(fā)進(jìn)行。標(biāo)準(zhǔn)焓變?yōu)檎担砻髟摻到膺^程為吸熱反應(yīng),溫度升高有利于降解進(jìn)行,與2.2節(jié)的分析結(jié)果吻合。標(biāo)準(zhǔn)熵變?yōu)檎担砻鳠峄罨?,過硫酸鹽及柴油相界面的混亂度有增加的趨勢(shì),接觸幾率增加,有助于反應(yīng)進(jìn)行。根據(jù)表觀反應(yīng)速率常數(shù)計(jì)算得到,熱活化過硫酸鹽降解柴油污染土壤的表觀活化能為-80.73 kJ/mol。
圖4 初始pH對(duì)柴油降解率的影響Fig.4 Effect of initial pH on the degradation efficiency of diesel oil
圖5 降解過程中pH的變化Fig.5 The varation of pH during the reaction process
(1) 當(dāng)Na2S2O8摩爾濃度為0.8 mmol/g、溫度為70 ℃、水土比為2.0 mg/L、初始pH為11.00時(shí),柴油降解率最高,為77.85%。
表1 動(dòng)力學(xué)和熱力學(xué)參數(shù)
(2) 熱活化過硫酸鹽氧化降解柴油過程為自發(fā)、吸熱、熵增的過程,表觀活化能為-80.73 kJ/mol。
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Thermoactivatedpersulfateoxidationforremediationofdieseloilcontaminatedsoil
LIYongtao,LUOJin,YUEDong.
(SchoolofChemistryandChemicalEngineering,SouthwestPetroleumUniversity,ChengduSichuan610500)
Thermo activated persulfate oxidation was selected to repair diesel oil contaminated soil. The effects of concentration of persulfate,temperature,water-soil ratio,and initial pH on the degradation efficiency of diesel oil were investigated,and kinetic and thermodynamic parameters were analyzed. Results showed that the degradation efficiency of diesel oil reached peak (77.85%) when Na2S2O8molar concentration was 0.8 mmol/g,temperature was 70 ℃,water-soil ratio was 2.0 mL/g,and initial pH was 11.00 after 72 h. According to the kinetic and thermodynamic analysis,it was showed that the remediation process could occur spontaneously. The oxidation process was a endothermic and entropy-increasing reaction with an apparent activation energy of -80.73 kJ/mol.
10.15985/j.cnki.1001-3865.2017.10.021
李永濤,男,1977年生,博士,副教授,主要從事油氣田環(huán)境污染防治與地下水環(huán)境保護(hù)研究。
2016-11-07)