Interpretation of the acid-base equilibrium of humic acid by a continuous pK distribution and electrostatic model

Interaction study between Ca2+ and humic acids in brine media

“…In [8] the concentration of the phenol group was reported to be 2.26 ± 0.72 (pK a unknown). Our results compare well with values (pK a values given at α HA = 0.5) of humic acids extracted from soils or waters [2,[9][10][11][12][13][14] or purchased from other companies (Wako [15], Fluka [16] and between 2.0 and 3.0 meq/g for the weaker sites (with pK a values from 5.0 to 6.4). Measurements of phenolic groups have not been reported as frequently but the capacity values for the phenolic groups range from 0.8 to 4.3 meq/g, while their pK a values vary from 8.9 ± 0.1 to 9.0 ± 0.2.…”

Determination of Co(II) and Ni(II)-humate stability constants at high ionic strength NaCl solutions

“…Data points were recorded in mV units and converted into pcH (= − log[H + ], where [H + ] is the concentration of H + ). All titrations were performed using a "back-titration" method (Fukushima et al, 1995;Fukushima et al, 1996) under an atmosphere of N 2 (g) in a magnetically stirred, closed thermostatted cup at 25.0 ± 0.1 • C. Four titrations of humic acid were performed at each ionic strength of 0.1 m, 0.3 m, 1 m, 3 m and 5 m NaCl. Prior to each humic acid titration, a potentiometric titration of a carbonate-free, 0.04 M NaOH solution with a 0.04 M HCl solution was performed at the same ionic strength as the HA titration.…”

Evaluation of Copper(II) Binding Abilities of Humic Substances by a Continuous Site-Distribution Model Considering Proton Competition

“…A typical example of this interpretation is the Scatchard-plot method. 7,10,11 Moreover, the continuous-site distribution models [12][13][14][15] , in which the stability of metal binding sites is assumed to distribute continuously, have been used in interpreting the metal binding equilibria of heterogeneous polyelectrolytes, such as proteins and HSs. The discrete-site models cannot always represent the actual binding manner 4,6 , whereas the continuous-site distribution models reflect the actual distribution of the stability of the metal binding sites in the humic molecule.…”