DOES ORGANIC-ACID ADSORPTION AFFECT ALKALI-FELDSPAR DISSOLUTION RATES

Consideration of alkali-feldspar dissolution rates(1) taken from the l iterature suggests that in the absence of organic ligands and at far f rom equilibrium conditions they can be represented by r(+)= k(a(H)(3)/a(Al)(+3))(n), where r(+) refers to the far from equilibrium dissolut ion rate, k designates a rate constant, a(i) stands for the activity o f the subscripted aqueous species, and n refers to a stoichiometric co efficient. Dissolution rates of these minerals have also been observed to increase substantially with increasing aqueous organic acid concen tration. To assess if this latter effect is the result of either the c hange in aqueous aluminum activity due to aqueous aluminum-organic aci d anion complex formation or organic acid anion adsorption to the mine ral surface, dissolution rates predicted using the above equation are compared to measured alkali feldspar dissolution rates. A close corres pondence between these predictions and the experimental data are found , providing strong evidence that organic acid anion adsorption does no t affect alkali-feldspar dissolution rates. (C) 1998 Elsevier Science B.V. All rights reserved.