COl6-7037/93/$6.00 + .oO Gmchmm d Cosmochimica Acln Vol. 57. p. II57 Copyright 0 1993 Pergamon Press Ltd.Pnnted in U.S.A zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA REPLY Reply to the Comment on “Speciation of aqueous palladium(I1) chloride solutions using optical spectroscopies” C. DREW TAIT and DAVID R. JANECKY Los Alamos National Laboratory, INC Division, MS-J514, Los Alamos, NM 87545, USA (Received September 8, 1992; accepted in revised form September 25, 1992 ) neutral chloride solutions, but for concentrated Pd (3 mM). THE THOUGHTFULCRITICALComment of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA BYRNE and KUMP Furthermore, they report a chloride-free Pd precipitate, in( 1993 ) presents different opinions/ interpretations to two dicating continued loss of Cl- after the formation of Pdprevious works on palladium speciation, namely TAIT et al. C&OH *- . Therefore, the reaction associated with the observed ( 199 1) and WOOD ( 199 1) . In essence it argues that the exslow kinetics cannot be proven to be polymerization or further perimental data in each of these papers should be taken more hydrolysis. Even if the reaction is polymerization, it may at face value than the original authors did. BYRNEand KUMP suggest that the mixed chlorohydroxy palladium species are ( 1993) present arguments to show that the presence of mixed not stable, with the chlorides ultimately being replaced by ligand chlorohydroxypalladium (II) complexes extends to low (bridging) oxygens. concentrations relevant to seawater (in contrast to a concluThe identity of the slow reaction beyond the formation of sion of TAIT et al., ( 199 1) and that the hydrolysis constants PdC&OH *- remains an important but unanswered question. measured by WOOD ( 1991) are in fact not too small and should not be rationalized away. The self-consistency of the Even if colloid is forming under the conditions which have equilibrium values presented in the BYRNEand KUMP ( 1993) been examined experimentally, it may still represent the end comment is very alluring, especially when they are achieved of a reaction in which the chlorides are replaced by hydroxide from both statistical predictions and linear free energy relabefore polymerization, and hence call into question what actions. Several interesting and valid points are made by BYRNE tually happens under the lower Pd concentrations of seawater. and KUMP (1993), but perhaps some counterpoints should Indeed, the Comment of BYRNE and KUMP (1993) notes be considered. We would like to respond to the comments the possibility of unusually slow kinetics for Pd(OH)* formade on our previous paper. mation, although they do not favor this explanation. This As noted in their Comment BYRNE and KUMP (1993), Reply basically attempts to underline this possibility. Ultiwe dutifully reported mixed Pd-Cl-OH complexes under the mately, as noted by KUMP and BYRNE (1989), inorganic given experimental conditions. In fact, our Fig. 4a gives direct palladium speciation may be eclipsed by organic complexspectral evidence for the mixed complexes and strongly ation in some and perhaps many natural environments, inbacks up the inferred evidence from curve fitting of KUMP cluding in seawater. The case for hydroxy-pseudocolloids and BYRNE ( 1989). However, we closely observed two dif(Pd( OH), attachment to organic colloids) may also be made. ferent palladium concentrations (124 PM and 3 PM) and Thus, while we appreciate the self-consistency from different observed less evidence for the mixed complexes at lower conapproaches and the detailed analyses of BYRNE and KUMP centration. We, therefore, felt that extrapolation to even lower ( 1993), we feel there is still some room to suspect that Pd Pd concentrations relevant to seawater was not warranted. behavior and complexation is not quite as neat as presented BYRNE and KUMP ( 1993) are correct in pointing out that by BYRNEand KUMP ( 1993), and that extrapolation to seaOH- is not a thermodynamically limiting reagent (with OHwater systems may still present some difficulties. Editorial handling: G. Faure being available from water from hydrolysis reaction with the metal), but in our view it could be a kinetically limiting REFERENCES factor. We (as well as others: e.g., KAZAKOVAand ~ITSYN, 1967; BYRNER. H. and KUMPL. R. ( 1993) Comment on “Speciation of NABIVANETSand KALABINA,1970) reported a slow chemical aqueous palladium (II) chloride solutions using optical spectroscopies” by C. D. TAIT, D. R. JANECKY, and P. S. Z. ROGERS. reaction from pH changes, absorbance changes, and the Geochim. Cosmochim. Acta 57, 115 1-l 156 (this issue). appearance of precipitate at higher Pd concentrations. KMAKO~A V. I. and PTITSYN B. V. ( 1967) Hydrolysis of halogenoWe interpreted this slow reaction as continued hydrolysis complexes of palladium. Russ. .I. Inorg. Chem. 12, 323-326. beyond the quickly forming PdC130H2- (i.e., PdC130H2KUMP L. R. and BYRNE R. H. ( 1989) Palladium chemistry in seawater. Environ. Sci. Tech. 23, 663-665. + OH- - + Pd(OH)2 + 3Cl-), while BYRNEand KUMP NABIVANETS B. I. and KALABINA L. V. ( 1970) State of palladium ( 1993 ) assign it to a polymerization reaction that would not (II) ion in perchlorate solutions. Russ. J. Inorg. Chem. 15, 8 18occur at the low Pd concentrations found in seawater and 821. hence would not further affect the PdC130H2- initially TAIT C. D., JANECKY D. R., and ROGERS P. S. Z. ( 199 1) Smiation of aqueous palladium (II) chloride solutions using optical specformed. While BYRNE and KUMP ( 1993) cite NABIVANETS troscopies. Geochim. Cosmochim. Acta 55, 1253-1264. WOOD S. A. ( 199 1) Experimental determination of the hydrolysis constants of Pt2+ and Pd2+ at 25°C from the solubility of Pt and Pd in aqueous hydroxide solutions. Geochim. Cosmochim. Acta 55, 1759-1767. and KALABINA ( 1970) as a reference to polymerization, NABIVANETS and KALABINA ( 1970) only showed polymerization for acidic, non-Cl_ solutions with [ Pd] > 10 PM. KAZAKOVA and PTITSYN ( 1967) also mention polymerization for near1157