Trilon® D Liquid - the Performance Chemicals division - BASF.com

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TI/EVD 1116 e January 2007 Page of 8 Trilon D Liquid300Viscosity mPa·s250Trilon D Liquid200150100500-10 0 10 20 30Temperature (°C)Viscosity as a function of temperatureComplex formationThe most important property of Trilon D Liquid is its ability to form watersolublecomplexes with polyvalent ions (eg. calcium, magnesium, lead, copper, zinc, cadmium, mercury, manganese, iron, aluminium) over a widepH range from 2 to 13.5. HEDTA usually forms 1 : 1 complexes, i. e. 1 mol ofHEDTA chelates binds to 1 mol of metal ions. The metal ion is completelyenclosed by the ligand. These complexes remain stable, especially in alkalimedia and even at temperatures of up to 100 °C. [MeZ (m-n)- ]K = ––––––––––––– [Me n+ ] [Z m- ]From the law of mass action, the equation for the stability constant K for1 : 1 complexes can be written as follows:where[MeZ (m-n)- ][Me n+ ]is the concentration of the chelate that is formedis the concentration of free, positively charged metalions[Z m- ] is the concentration of the ligand anion, in this caseHEDTAKis the stability constant for the chelate.
TI/EVD 1116 e January 2007 Page of 8 Trilon D LiquidLogarithmic stability constants (log K) for complexes of HEDTA and selectedmetal ionsMetal ionlog KFe 3+ 19.8Cu 2+ 17.5Ni 2+ 17.1Zn 2+ 14.6Fe 2+ 12.2Mn 2+ 10.8Ca 2+ 8.2Mg 2+ 7.0HEDTA-H 3is a tribasic acid that dissociates in three steps. The acid dissociation constants pK aare as follows.HEDTA-H 3 pK a 1 2.6HEDTA-H- 2 pK a 2 5.3HEDTA-H 2- pK a 3 9.7In aqueous solutions, HEDTA competes for metal ions with other anionssuch as hydroxide, sulphate, sulphide, carbonate and oxalate that formsparingly soluble metal salts. The formation of chelates reduces the concentrationof free metal ions [Me n+ ] to such an extent that the solubility productsof many sparingly soluble metal salts are no longer exceeded. The result isthat the salts no longer precipitate or may even redissolve.The high stability of these complexes prevents the metal ions from participatingin typical chemical reactions. For instance, manganese, iron and copper are no longer able to catalyse the decomposition of peroxide bleach.Conditional stability constants [log K cond] take into account the stability constant K as well as the acid base dissociation equilibria.16log K cond14121086420Ca 2+Cu 2+Fe 3+Mg 2+Mn 2+0 2 4 6 8 10 12 14pHConditional stability constants for selected HEDTA chelates
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