Study on surface acid2base properties of Chinese loess

23 1 2003 1 ACTA SCIENTIAE CIRCUMSTANTIAE Vol. 23,No. 1 Jan.,2003 :025322468 (2003)20120006205 :X13113 :A 1, 1, 1, 2, 2, 2, 2 (11,, 100085 ;2., 030006) :,.., (011 molπl) (0101 01005 molπl). : ; ; ; ; Study on surface acid2base properties of Chinese loess LIU Wenxin 1, CHU Zhaosheng 1, TANG Hongxiao 1, QIAN Tianwei 2, LI Shushen 2, LI Zhenting 2, WU Guibin 2 (1. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco2Environmental Sciences, Chinese Academy of Sci2 ences, Beijing 100085 ; 2. China Institute for Radiation Protection, Taiyuan 030006) Abstract :Titration was used to study the surface acid2base characteristics of a Chinese loess sample at different concentrations of supporting electrolyte. The acidimetric supernatant was considered as the system blank to compensate the influence of particle dissolution and complex re2 actions between soluble components on estimation of proton consumption. The simulation results of two simple surface complexation models in2 dicated that the constant capacitance model and the diffuse layer model were applicable to the high ionic strength (011 molπl) and to the low ionic strengths (0101 and 01005 molπl), respectively. Keywords :Chinese loess ; acid2base titration ; surface proton reaction ; constant capacitance model ; diffuse layer model 2 [1 ].,,., [2 ],,,., [3 ],,.,,.,. 1 111. 63 m. X (3080E 2,RIGAKU) :SiO 2 (5811 %) Al 2 O 3 (1113 %) CaO(913 %). N 2 ΠBET (ASAP 2000,Micrometrics) :2002203228 ; :2002206225 :(20037010) : (1967 ),,

1 : 7 14181 m 2 Πg. 10 gπl 4,. NaOH (010455 molπl), (010953 molπl) NaOH. 112 (Microprocessor 682,Metrohm). NaNO 3 (110 molπl) 5 gπl. 01005 01010 01100 molπl NaNO 3., N 2. 1 h, : ph 315 ( ), 0101 mlπmin NaOH ph 10 ( ). 10000 rπmin 30 min,. 2 ( ICP2AES,ULTIMA,Jobin Yvon Emission,Horiba Group). 2 211 1.,, ph, OH -,., [4 ]. 1 Fig. 1 Titration curves of the sample and blank at different ionic strengths. The solid and open symbols represent the titration points of the sample and blank at different ionic strengths, respectively 212 (TOTH) ( H S ) [4 ], ( V e ), TOTH H S. 2,., ( )., ( G) : : G a = ( V 0 + V at + V b ) 10 - ph 100 (1) : G b = ( V 0 + V at + V b ) 10 - (1318 - ph) 100 (2) V 0,V at V b., OH - H + ( V eb1 V eb1 ) ( V eb1 V eb2 V eb1 V eb2 ) ph( V eb2 V eb2

8 23 2 Fig. 2 (, ) Gran plots of the sample and blank at different ionic strengths. The open squares and triangles represent the titration data on sample and blank at the acidic side, respectively. The filled squares and triangles denote the titration data on sample and blank at the alkaline side, respec2 tively. 213 ). V eb1 V eb1 V eb2 V eb2. V eb1, OH -, (zero point of titration,zpt)., H + : TOTH = - ( V b - V eb1 ) C b (molπl) (3) V 0 + V at + V b C b NaOH. ZPT (FITEQL 210 [5 ] )., H + : 21311 ( 1 ) H +,,. [3 ],. H R = [ TOTH - 10 - ph + 10 - (p K W - ph) ] ( H R ) ( V 0 + V at + V b ) (mol) (4) ph K W - log[ H + ] 011 molπl (p K W = 1318). ( H S ) ( D S ),, H S D S, [6 ],, H S, 5 : H S = ( V eb2 - V eb1 ) sample C b - ( V eb2 V 0 - V eb1 ) blank C b (molπl) (5) 01005 01010 01100 molπl NaNO 3, H S 118 10-4 210 10-4 117 10-4 molπl., FITEQL 1 Table 1 Concentrations of soluble Si and Al in the acidimetric supernatant (NaNO 3 ), molπl Si, molπl Al, molπl 01005 1146 10-4 4111 10-5 01010 1132 10-4 3189 10-5 01100 8110 10-5 3199 10-5, (hydroxyaluminosilicate,has) [7 ]., HAS : pal 3+ 3 p- q- r + qh 4 SiO 4 + rh 2 O Al p (OH) r (OSi (OH) 3 ) q + ( q + r) H + (6) p q r.,, :

1 : 9 Al 3+ + H 4 SiO 4 Al (OSi (OH) 3 ) 2+ + H + (7) HAS 2. 3,. 21312 [3 ],, ( ),,, H S. V eb, 2 FITEQL Table 2 Chemical reactions considered in the FITEQL calculation [8 ] Al 3 + + H 2 O AlOH 2 + + H + log K = - 5152 (25, I = 011) Al 3 + + 2H 2 O Al (OH) + 2 + 2H + log K = - 10140 (25, I = 011) Al 3 + + 3H 2 O Al (OH) 3 + 3H + log K = - 16130 (25, I = 011) Al 3 + + 4H 2 O Al (OH) - 4 + 4H + log K = - 23100 (25, I = 0101) Si (OH) 4 SiO(OH) - 3 + H + log K = - 9146 (25, I = 015) Si (OH) - 3 SiO(OH) 2-2 + 2H + log K = - 22102 (25, I = 015) Al 3 + + H 4 SiO 4 Al (OSi (OH) 3 ) 2 + + H + log K f = - 2174 SOH SO - + H + p K int a SOH + Al 3 + + H 4 SiO 4 SOAl (OSi (OH) + 3 ) + 2H + p K SC I. 3 Fig. 3 ( 01005 0101 011 molπl NaNO 3 ) Model description and actual titration data of the system blank at different ionic strengths. The dotted, dashed and solid lines represent model simulation results at 01005, 0101 and 011 molπl NaNO 3, respectively ph H R ( 4 ), : SOH SO - + H + (8), : SOH + Al 3+ + H 4 SiO 4 SOAl (OSi (OH) + 3 ) + 2H + (9), 2., (constant capacitance model,ccm) [9 ].,CCM (diffuse layer model,dlm). DLM, (011 molπl ),, DLM [9 ]., CCM DLM. 3 4. ( V Y ). CCM DLM.,.,., CCM DLM

10 23 4 ( CCM DLM ) Fig. 4 Model description of the sample at differ2 : ent ionic strengths. The solid and dashed lines represent simulation results using CCM and DLM, respectively, (011 molπl NaNO 3 ), (01005 0101 molπl NaNO 3 ). 3 Table 3 Surface characteristic parameters of the loess sample NaNO 3, molπl C P = 5 gπl, SSA = 14181 m 2 Πg, D a S = 118 Πnm 2, FΠm 2 V Y p K int a SD (p K int a ) b p K SC SD (p K SC ) b 01005 1160 2213 5101 0102 2149 0105 01010 2100 2515 5103 0102 2119 0105 01100 1155 612 3198 0102 3148 0107 01005 2718 3148 0102 4104 0104 01010 3010 3155 0102 3180 0104 01100 914 3190 0102 2178 0104 a1 D S = ( H S N A )Π( C P SSA 10 18 ) N A Avogadro (61022 10 23 Πmol), C p b1 SD 3 11,. 21, (011 molπl NaNO 3 ) (0101 01005 molπl NaNO 3 ). ( 20011108200578),. [ 1 ] Stumm W. Chemistry of the solid2water interface : Processes at the mineral2water and particle2water interface in natural systems [M]. Stumm W. (eds. ), New York : Wiley, 1992 [ 2 ] Wen X H, et al. Surface complexation model for the heavy metal adsorption on natural sediment [J ]. Environ Sci Technol, 1998, 32 : 870 [ 3 ] Liu D S. Loess and Environment [M]. Beijing : Science Press, 1985 [ 4 ] Liu W X, et al. A comparative study of acid(base characteristics of natural illites from different origins [J ]. J Colloid Interface Sci, 1999, 219 : 48 [ 5 ] Westall J C. FITEQL : A computer program for determination chemical equilibrium constants from experiment data [ R ]. Version 210. Report 82202, Department of Chemistry, Oregon State University, Corvallis, OR, U. S. A., 1982 [ 6 ] Davis J A, et al. Application of the surface complexation concept to complex mineral assemblages [J ]. Environ Sci Technol, 1998, 32 : 2820 [ 7 ] Browne B A and Driscoll C T. Soluble aluminum silicates : Stoichiometry, stability and implications for environmental geochemistry [J ]. Science, 1992, 256 : 1667 [8 ] Smith R M, Martell A E. Critical stability constants, Volume 4 : Inorganic complexes [M]. New York : Plenum, 1976 [ 9 ] L tzenkirchen J. Parameter estimation for the constant capacitance surface complexation model : analysis of parameter interdependen2 cies [J ]. J Colloid Interface Sci, 1999, 210 : 384