Correlating metal ionic characteristics with biosorption capacity of Staphylococcus saprophyticus BMSZ711 using QICAR model

Quantitative Ion Character–Activity Relationship (QICAR) was used for correlating metal ionic properties with maximum biosorption capacity ( q max). Heat inactivated biomass of Staphylococcus saprophyticus BMSZ711 was studied for biosorption of nine metal ions. Influence of contact time and initial pH was checked. q max was determined by Langmuir isotherm and followed a descending sequence (in mmol/g): Pb 2+ > Cd 2+ > Cr 3+ > Zn 2+ > Hg 2+ > Cu 2+ > Co 2+ > Ni 2+ > K +. q max values was modeled with 20 metal ionic characteristics, among these covalent index ( X m 2 r) was best fitted with q max for all metal ions tested, in the following model: q max = 0.09 + 0.11( X m 2 r) ( R 2 = 0.73, AIC = −4.14). Classification of metal ions according to valence or soft/hard improved QICARs modeling and more characteristics significantly correlated with q max which revealed that covalent bonding played major role in biosorption of soft metal ions and ionic bonding for borderline and hard ions. Biosorption capacity was most effectively predicted (R 2 = 0.99, AIC = −8.04) with a two variable model containing electro-negativity ( X m) and softness index ( o ρ ′ ) .