Applications of Water Sensitivity In Situ Remediation at Saltwater-Freshwater Interface

Trans. Tianjin Univ. 2009, 15: 150-155DOI 10. 1007/s1 2209-009-0077-01。 Tianin University and Springer-Verlag 2009Applications of Water Sensitivity In Situ Remediationat Saltwater- Freshwater Interface”HAN Zhiyong (韩志勇)'，ZHENG Xilai(郑西米)'，CHEN Jihong (陈继红)2(1. Institute of Environment Scicnce and Engineering, Ocean University of China, Qingdao 266003, China;2. College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, China)Abstract: Based on the laboratory experiments with the saltwater and freshwater replacing each other in the levelsand column, taking the kaolin, ilite, smectite, bivalent hydrargyrum ion (Hg*) and phenol (CgH3OH) as exam-ples, this paper studies the applications of water sensitivity in situ remediation in saltwater-freshwater transitionzone. In the water sensitivity process, the release and migration of clay minerals can make the hydraulic conductiv-ity (HC) decrease and pollutants remove. A new type of low penetrable or impenetrable purdah can be built byadding clay minerals into the sand media to replace the underground concrete impenetrable wall to prevent seawaterintrusion, and a number of the heavy metals and organic pollutants in the sand media can be removed by in situremediation. The results show that the content of kaolin and ilite influences the water sensitivity process slightly,and HC of the sand columns descends from 0.011 cm/s to 0.001 4 cm/s and 0.001 2 cm/s respectively even if thecontent reaches 12% (weight ratio, sic passim) . However, for smectite, HC descends sharply to about 1x10* cm/swhen its content reaches 4%, and no water can flow through the sand columns beyond 5%. The particle release andmigration processes can remove the Hg2' and C.HzOH out of the sand columns efficiently, the removing rate ofHg' is 31.68% when the freshwater and saltwater are filtered through the sand columns polluted by Hg2 , while it is67.55% when the water sensitivity occurs. With the same method, the removing rates of CHsOH under the fluidflow and water sensitivity are 55.71% and 43. 43% respectively.Keywords: saltwater-feshwater interface; water sensitivity; in situ remediation; bydraulic conductivityThe dependence of permeability on the composition of sensitivity of sandstones which contained swelling and non-the flowing fluids is known as water sensitivity'". Since swelling clay minerals and indicated that the different oneswater sensitivity was discovered, it has been studied for had different water sensitivity characters and mechanisms,more than 70 years in several fields such as petroleum in- and it is one of the most important reasons for the waterdustry, geotechnical engineering and landfill remediation, sensitivity of the porous medial.and there has been a common agreement that the particleThe studies of the applications of water sensitivity fo-release, migration, re-deposition and recapture are the re-cused on the fields of petroleum industry, geotechnical ensults of water sensitivity". Most of the studies were focused gineering and andfill remediation to search for some efi-on the mechanisms of the water sensitivity. For example,cient methods for higher production efficiency, higher imi-Khilar showed that the phenomenon of colloidalinduced gating seepage and lower permeability than common condi-fines migration was of significant importance in the petro- tions respectively. Gruesbeck, Kia and Khilar et al studiedleum industry as these released fines could migrate and plug the influence factors of water sensitivity by the experimentsregions in the formation, causing damage and hence reduc- of the Berea sandstone, and put forward some measures totion in production2. Ryan summed up that the response of avoid the ocurrence of water sensitivity in the process ofclay in contact with aqueous fluids was a fundamental prob- oil and gas exploitation'5-T. Frenkel, Zheng and Xiao et allem that had an impact in a number of areas such as landfill found that low mineralization degree and high SAR canremediation, coastal encroachment, contaminant migration make the hydraulic conductivity (HC) of the soil decreaseand petroleum production and there had been no in-depth obviol中国煤化工ce to avoid the waterstudies of the above problems3]. Mohan studied the water sensit:YHCNMHGAccepted date: 2008-01-25.*Supporcd by National Natural Science Foundation of China (No.40572142).HAN Zhiyong. bom in 1976, male, Dr, associatc Prof.Corespondence to HAN Zhiyong, E-mail:hanzhy_ 009@sina com.HAN Zhiyong et al: Applications of Water Sensitivity In Siu Remediation at Saltwater Freshwater InterfaceIn coastal area, there is a transition zone (a long and1ExperimentsnarTow belt) under the ground between freshwater and sea-water, and when the hydrochemical or hydrodynamic con-1.1 Materialsditions change (e.g. freshwater replaces seawater), waterThe sand samples used in these experiments are fromsensitivity will occur. Goldberg and Mageritz found the sea- the profile of sand bed in the downstream area of Daguwater-freshwater interface in one of the Isracel areas had ob River, Qingdao, China, which is 18 km away from Jiaozhouvious water sensitivity when the freshwater replaced the Gulf. Granularity analysis experiment by the Laser Granu-seawaterl".. However, there are few studies of water sensi- larity Meter (MS2000) indicates that the weight ratio of thetivity of the coastal aquifer and no study of the applications sand whose diameter is less than 1 mm is 89.58%, less thanin transition zone.0.01 mm is 7.63% and less than 0.001 mm is 0.79% (parti-At Dagu River downstream, which is a seawater intru- cle) .sion area and 18 km away from Jiaozhou Gulf, QingdaoThe X-ray diffraction (D/max-T B-type Anode Cir-area, China, the seawater intrudes the freshwater aquifer cumgyration Diffraction Meter) measurement of the sam-from Jiaozhou Gulf by above 80 km', and some areas, such ples indicates that the framework grain is silicon dioxide,as Ligezhuang and Laixi, have been polluted by some heavy and the clay minerals are ilite (0.12%), kaolin (0.7%),metals and organic wastewater. In order to prevent the sea- chlorite (<0.1%) and smectite (0.45%) .water intrusion, an underground concrete impenetrable wallThe water used in the experiment is freshwater and(3.5 km in width, 5- -7 m in thickness) was built in 1998，seawater, which was fetched from the downsteam area ofand it cost 20 millions RMB. At the same time, there areno Dagu River and Jiaozhou Gulf respectively. The mainefficient methods to treat the heavy metals and organic ma- chermical components and conductance determined by theterials in the aquifer.Agilent 3510 atom-absorbency spectrophotometer andIn this paper, the water sensitivity characters of the Dionex DX-80 ion-chromatogram column are listed inoriginal and clay-sand samples are studied first to make a Tab.1. The working conditions of the Agilent 3510 atom-contrast, and the feasibility of building low-penetrable or absorbency spectrophotometer are as fllows: light current 3impenetrable purdah underground is studied to replace the MA, slot 0.1 mm, air flux 400 L/h, acetylene flux 25 Lh,underground concrete impetrable wall to prevent the sea- buming implement 10 mm and expansion coffcient 2, andwater intrusion in seawater-freshwater transition zone. Then the absorbency wavelengths for the elements K, Ca, Na anda series of experiments are designed to study the applica- Mg are 404.4 nm, 422.7 nm , 330.3 nm and 285.2 nm re-tions of water sensitivity to remove the pollutants out of the spetively. The DX- 80 ion-chromatogram colums used areseawater-freshwater transition zone by the carrying effects ASI4A high efficiency anion analysis column (3 mmx150of particle release and migration. This paper provides an in mm) and AG14 protection column with the highest pumpsitu remediation method for coastal environment protection pressure 3 000 psi (21 MPa) and flow velocity 0.5- 4.0and other fields.mL/min.Tab.1 Chemical compositions and conductance of seawater and freshwater samplesNa*K*/Ca2*/Mg*+/C1/SO2/HCO,/Eletric conductivity/(mg:LI)_ (mg:L')___ (mg:LI)__ (mg L 1)(mgL 1)(mg:L)__ (mg L 1)(uscm 1)Seawater8S34.78418.09289.301 094.9818 220.71648 S00Freshwater69.406.3556.4614.34121.77131.4687.696761.2 Experimental installationwith clay was mixed using Vortex -Genie Vibration MeterThe experimental installation (Fig.1) is composed of and its density is about 1.57 g/cm'.stable hydraulic head water supply system (5 000 mL feed- 1.3 Methodswater bottle, feedwater pipe, pump, flume, stable hydraulic 1.3.1 Water sensitivity characters of different clayhead insalalation), sand column ( φ 2.4 cm x 25 cm organic中国煤化工glass pipe full of sand, plugs) and measurement system1.5%, 2%, 3%, 4%,(test tubes of 1, 5 and 10 mL, micro pressure meter). The 5%, 7.3MYHC NMHGe secte and sndhydraulic head in the experiment is 30 cm. The sand along were mixed respectively, and then were added into the or--15I-Transactions of Tianjin University Vol.15 No.2 2009ganic glass pipes (3 samples) and vibrated by Vortex-Genie ured; finally, the standard curve between Hg2* concentrationVibration Meter to be mixed uniformly, and their densities and absorbency was protracted.are 1.57, 1.58 and 1.58 g/cm'. Under the water head of 30 1.3.3 Removing of CH,OH by water sensitivitycm, the sand columns were saturated with seawater for 24 h,The experimental processes are similar to Sectionwhich was still used for filtering the sand columns. The 1 .3.2(3 samples) except that the mensuration method offlowrate and conductance of the outflow were measured till C6HzOH quantity is bromination titration.they were stable. Then the flowing fluid in the sand columnswas changed to the freshwater and the volume, hydraulic 2 Results and discussionhead loss (by micro-pressure meter) and conductance wererecorded in order to calculate the hydraulic conductivity by 2.1 Water sensitivity characters of different clayDarcy's Law and judge the stability of the outflow.mineralsThe experimental results indicate that the hydraulicconductivities of the kaolin-sand and ilite-sand systems0 J5vary unobviously but similarly, while the smectite-sand sys-tem varies greatly and acutely.12、12-(1) For all the clay-sand systems, with the clay con-8,12tents below 1.5%, HC has no obvious variations when onlythe seawater flows through the columns, and HC of thesmectite-sand system descends from 0.01 cm/s to 0.007 I1- Feedwater botle (5 000 mL);2- Plug: 3- Gilass pipe;4 -Pump; 5一cm/s when the clay content increases from 1.5% to 2%Flume; 6- Stable water-head pipe; 7- Water-stop clip; 8 Sand column;(Fig.2). But HC of kaolin and ilite sand systems descends. 9- -Test tube; 10- Fereous sieve (0.05 mm); 11- Glass siphon; 12- from 0.01 cm/s to 0.009 6 cm/s and 0.009 1 cm/s respec-Rubber pipe; 13- -Bracket; 14- Board; 15- Micro-pressure meter.tively (Fig.3 and Fig.4).Fig1 Sketch of experimental istallation(2) When the inflow is changed from seawater tofreshwater, water sensitivity arises and HC of the columns1.3.2 Removing of Hg2+ by water sensitivityvaries immediately. HC of ilitle and kaolin sand systemsThis experiment was to demonstrate that the releasingdescends to 0.001 4 cm/s and 0.001 2 cm/s respectivelyparticles carry the remnant polluted cations when the waterwhen the content increases to 12% (Fig.3 and Fig.4) . How-sensitivity occurs. The sand sample used in this experimentever, for the smectite -sand system, it descends to 1x10^8is the original one which has been filtrated by 2-mm screencm/s and 0 cm/s when the smectite contents are 4% and be-without the addition of any other materials. First, the sandyond 5% respectively (Fig.2).columns were saturated (3 samples) with the HgCl2 solu-0.012tion (0.003 mol/L) for 24 h. Then the freshwater and sca-0.010t Frahwaterwater flowed into them in turm, and the absorbency of thet Seawater.008+outflow was measured by ultraviolet-spectrophotometryE 0.006-method with UV-2100 spectrophotometer and the concen-s 0.004tration and quantity of the Hg* were calculated by absor-bency-Hg2' standard curve. When the quantity of the Hg2*0.002flowing with the freshwater descended to 0, the seawaterflowed into the columns. After that, the inflow was changedContent/%Fig.2 Variety of HC of smectite-sand system in waterto the freshwater to induce the water sensitivity occurringsensitivity processand the absorbency was measured too. Finally, the aboveThe essential reason for the different variations of HCprocess was repeated.The absorbency-Hg* standard curve could be obtainedin different clay mineral-sand systems is the differenceamon: the first process, whenwith the following method. Different concentrations of'only中国煤化工sand columns, the rea-HgCl2 solutions(5, 10, 15, 20, 25, 30 and 35 ug/L) are con-son fYC N M H Gthe clay minerals con-fected with chloroform and their absorbencies were meas- gest ana drenblockune pore canals and the higher the clay- -152-HAN Zhiyong et al: Applications of Water Sensitivity In Situ Remediation at Salrwater. Freshwater Interface0.012that the smectite aglomerates' volumes augment by 5- -100.010士Freahwatertimes and present different shapes, such as reticulation, an0.008tenniform, which flls in the pore spaces and diminishes thes 0.006water flow area greatly.0.0042.2 Removing of Hg2* by water sensitivity0.002In the experiments, the average total quantity of Hg2+removed in the sand-column is 0.064 4 g(0.0642 g, 0.064 5g, 0.064 5 g) according to the solution volume. When onlyFig.3 Variety of HC of kaolin-sand system inthe freshwater flowed through the sand columns, Hg2”withwater sensitivity processthe average quantity of 0.0204 g (0.020 2 g, 0.0205 g,0.020 6 g) was washed out of the sand columns with the- + Freshe ater+ Seawaleraverage proportion 31 .68%(31.47%, 31.78%, 31.78%) after60 min and average 594 mL freshwater flowed out (Fig.5) .自0.008Then the seawater flowed into the sand columns to replace重006the freshwater, but there was no added Hg° flowing out ofthe sand columns after 30 min and average 297 mL seawaterflowed in (Fig.5). After that, the freshwater flowed into theConirn/%8102sand columns again to result in the occurrence of water sen-sitity, and the quantity of Hg* flowing out of the sandFig.4 Variety of HC of ilite-sand system in watercolumns increased acutely by twice the former after only 10sensitivity processmin. After the other 130 min and average 1 054 mL fresh-content, the lower the HC. In the kaolin-sand system, thewater was used, the average total Hg2* quantity flowing outsingle kaolin minerals whose diameters are about or below of the sand columns is 0.043 5 g(0.043 3 g, 0.043 6 g,12 pum can move with the seawater freely, while the bigger 0.043 6 g) , and the average proportion is 67.55% (67.45%,ones whose diameters are about or beyond 20 um will coil 67.60%， 67.60%) (Fig.5). With the liquid changing intoor accumulate and enter the joint pores between the grains seawater again, no added Hg2+ flowed out of the sand col-as one part of the system (bridge effect). The actual fluid umns after 30 min and 189 mL seawater flowed in (Fig.5).area diminishes and HC descends, which is called dynamic After the above two processes, the average proportion ofdescendinglo. At the same time, the analysis result of XRD Hg2* removed is 99.23% in all.and electron microscope indicates that most of the kaolin100fminerals disperse and a few are absorbed loosely on the pore9(80surface or act as the flling of the grains. For the ilitle andsmectite minerals, most of them adhere to the pore surfaceE 40closely as the link of grains and form a clay coat on the30grain surface (coating effect) . When the fluid flows by the& 20ilite and smectite minerals, a stable hydratation membrane1(;050 100 150 200 250forms on the mineral surface gradually, which makes theTime/miopore area diminish and HC descend, and it is called staticFig.5 Removal effects of Hg2+ by seawater andhydraulic conductivity descending14.3]. Moreover, the hy-water sensitivity effctsdratation membrane of the smectite mineral is much thickerFor the Hg2* ions in the sand columns, part of them de-(>10 times) than that of the ilite mineral, which is the otherposit on the sand surface by the gravity and form an unsta-important reason for HC descending. However, as the reac-ble sand-ion system which can be destroyed easily only bytive mineral, the most primary reason which can cause HCwater flow, and it is the reason why the single seawater ef-of the smectite -sand system to descend sharply is that thereplacing process can induce the effects of crystal layerfect carAs we know,swelling and particles flocculating, resulting in the forma-there中国煤化Ierals with negativetion of the smectite agglomerates with larger volume andcharges:TYHC N M H Guble eletrode layerBingham yield value. The electron microscope results showwhich can absorb the Hg^* with positive charges strongly-153-Transactions of Tianjin University Vol.15 No.2 2009into its Stern layer. Due to the effect of static and van der remove part of CHsOH1S. Due to the effect of van derWaals attractions, a more stable sand-clay-ion system than W als attractions, a more stable sand -clay-C;HsOH systemthe sand-ion one forms, which cannot be destroyed only by than the sand-C6HyOH one forms, which cannot be de-water flov14.1. A large number of Hg2* ions are absorbed stroyed only by water flow. A large amount of C6HsOH areand deposit in the sand media. When water sensitivity OC-still absorbed and deposited in the sand mediall4. Whencurs, the sand-clay-ion system is separated into sand- and water sensitivity occurs, the sand-clay-C6HsOH system isclay-ion parts with the clay minerals releasing from the sand scparated into sand- and clay-CbHsOH parts with the claysurface, and the remnant Hg2* ions will flow out of the sand minerals releasing from the sand surface, and the remnantcolumns with the clay's migration. In order to prove theC6HgOH will flow out of the sand columns with the clay'scorrectness of the analysis of the experimental phenomenon, migrationlo. Like Section 2.2, an acentric experiment wasan acentric experiment is designed to separate the releasing designed and the result proves the correctness of the analy-particles from the outflow in water sensitivity experiment, sis of C6HzOH removed by the water sensitivity effect.and the result indicates that there is no Hg* in the upper100water, which can explain that all the remnant Hg^ ions areabsorbed by the clay minerals and migrate out of the sandcolumns along with them.2.3 Removing of CH,OH by water sensitivityIn the experiments, the average total quantity of; 20-C6HzOH removed in the sand-column is 0.035 0 g (0.034 310g, 0.034 8g, 0.035 9 g) according to the solution volume.05306090120150180210240270Time/minWhen only the freshwater or seawater flowed through theFig.6 Removal effect of C.HgOH by seawater andsand columns, 0.0195g (0.019 0g, 0.0193g, 0.020 1 g)water sensitivity effectsC6HsOH on average was washed out of the sand column andthe average proportion is 55.71% (55.39%, 55.74%, 5.99%)afer 120 min and average 1 141 mL liquid (freshwater.90 3 Conclusionsmin, average 801 mL; seawater: 30 min, average 340 mL)flowed out, and the seawater did not take the added C6HzOHFrom the experimental results, the water sensitivity inout of the sand columns. Then the freshwater flowed into situ remediation of the sand aquifer at the seawater-the sand columns again to result in the occurrence of water freshwater interface can be applied in fields such as sea-sensitivity, and the average quantity of CHzOH flowing out water intrusion prevention, removal of heavy metals ionsof the sand columns increased acutely from 0.019 5 g to and organic pollutants.0.0307g (0.0307g,0.031 1g, 0.0302g) in the fllow-(1)For diferent clay minerals, the water sensitivitying 30 min, and there was no C6H2OH in the outflow after character of the smectite is much more obvious and acuteanother 110 min and average 930 mL freshwater flowed out. than kaolin and ilite. When the content of smectite reachesThen the freshwater was replaced by the seawater, but no 4%, HC of the smectite -sand system will almost descend toadded CHsOH flowed out of the sand columns after 30 min 0 and can be regarded as an impenetrable sand layer. Weand averagc 197 mL seawater was used. In the replacing can make use of the water sensitivity character to build un-experiment by freshwater, most of the remnant CgHzOH，derground impenetrable purdah or wall to prevent seawater0.0152 g on average (0.015 0g, 0.015 0g, 0.015 6g)，intrusion at the seawater freshwater interface.was washed out of the sand column with the particles releas-(2)It is a good method to use the water sensitivitying and migrating (Fig.6), and the average proportion is character of the sand media to remove the low concentra-43.43% (43.73%, 43.10%, 43.45%). After the above two tion of heavy metal ions and organic pollutants such as Hg*processes, the proportion of CHzOH removed is 99.14% in and C6HsOH, and the removing rates are 99.23% andll.99.14% respectively.For C6H2OH in the sand columns, part of it deposits on中国煤化工:e in the removing ratethe sand surface by the gravity and forms an unstable sand- betwe.1.H.CN M H G!y the seawater fnowsC6H,OH system which can be destroyed easily only by wa- througn ue salu Coum.11 Icasun is that a large numberter flow, and it is the reason why the seawater effect can of negative charges exist on the clay surface and they ab--154-HAN Zhiyong et al: Applications of Water Sensitivity In Situ Remediation at Saltwater Freshwater Interfacesorb much more Hg2* than C6HsOH, resulting in the higherconductivity [J] . Soil Science Society of America Jour-removing rate of Hg2* than that of C6HzOH.nal, 1978, 42(1): 32-39.(4) The precision of the mensuration method may be[9] Zheng Xilai, Qian Hui. 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