Study on surface acid2base properties of Chinese loess

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1 ACTA SCIENTIAE CIRCUMSTANTIAE Vol. 23,No. 1 Jan.,2003 : (2003) :X13113 :A 1, 1, 1, 2, 2, 2, 2 (11,, ;2., ) :,.., (011 molπl) ( 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 ; 2. China Institute for Radiation Protection, Taiyuan ) 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 molπl), respectively. Keywords :Chinese loess ; acid2base titration ; surface proton reaction ; constant capacitance model ; diffuse layer model 2 [1 ].,,., [2 ],,,., [3 ],,.,,., m. X (3080E 2,RIGAKU) :SiO 2 (5811 %) Al 2 O 3 (1113 %) CaO(913 %). N 2 ΠBET (ASAP 2000,Micrometrics) : ; : :( ) : (1967 ),,

2 1 : m 2 Πg. 10 gπl 4,. NaOH ( molπl), ( molπl) NaOH. 112 (Microprocessor 682,Metrohm). NaNO 3 (110 molπl) 5 gπl molπl NaNO 3., N 2. 1 h, : ph 315 ( ), 0101 mlπmin NaOH ph 10 ( ) rπmin 30 min,. 2 ( ICP2AES,ULTIMA,Jobin Yvon Emission,Horiba Group) ,, 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 - ( 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

3 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 + : ( 1 ) H +,,. [3 ],. H R = [ TOTH ph (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) molπl NaNO 3, H S molπl., FITEQL 1 Table 1 Concentrations of soluble Si and Al in the acidimetric supernatant (NaNO 3 ), molπl Si, molπl Al, molπl , (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.,, :

4 1 : 9 Al 3+ + H 4 SiO 4 Al (OSi (OH) 3 ) 2+ + H + (7) HAS 2. 3, [3 ],, ( ),,, H S. V eb, 2 FITEQL Table 2 Chemical reactions considered in the FITEQL calculation [8 ] Al H 2 O AlOH H + log K = (25, I = 011) Al H 2 O Al (OH) H + log K = (25, I = 011) Al H 2 O Al (OH) 3 + 3H + log K = (25, I = 011) Al H 2 O Al (OH) H + log K = (25, I = 0101) Si (OH) 4 SiO(OH) H + log K = (25, I = 015) Si (OH) - 3 SiO(OH) H + log K = (25, I = 015) Al H 4 SiO 4 Al (OSi (OH) 3 ) H + log K f = SOH SO - + H + p K int a SOH + Al H 4 SiO 4 SOAl (OSi (OH) + 3 ) + 2H + p K SC I. 3 Fig. 3 ( 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 ( V Y ). CCM DLM.,.,., CCM DLM

5 ( 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 ), ( molπl NaNO 3 ). 3 Table 3 Surface characteristic parameters of the loess sample NaNO 3, molπl C P = 5 gπl, SSA = 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 a1 D S = ( H S N A )Π( C P SSA ) N A Avogadro ( Πmol), C p b1 SD 3 11,. 21, (011 molπl NaNO 3 ) ( molπl NaNO 3 ). ( ),. [ 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

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