Adsorption difference of Cu2+ on the compositely modified amphipathic maifanites

To determine the effect of compositely modified amphipathic clay on Cu2+ adsorption, 50% and 100% cation exchange capacity (CEC) of anionic polyacrylamide (PA in the modified amphipathic maifanite (M-50x)), citric acid (CA), ethylenediaminetetraacetic acid (ED in M-50x), and sodium dodecyl sulfate (SD in M-50x) were used to remodify the 50% CEC of dodecyl dimethyl betaine (BS-12 or BS)-modified maifanite (M-50BS) and form four types of compositely modified amphipathic maifanite (M-50x), such as M-50BS/PA (including M-50BS/50PA and M-50BS/100PA; the same goes for the other samples), M-50BS/CA, M-50BS/ED, and M-50BS/SD. The adsorption and thermodynamic characteristics of Cu2+ on the various compositely modified M-50BS were investigated by using the batch method, and the adsorption difference in the pH value, temperature, and ion strength were discussed. The results showed that (1) the adsorption isotherms of Cu2+ on the test samples were all "L" type and combined with the Langmuir model. The maximum adsorption amount of Cu2+ on the different samples changed between 109.09 and 200.87 mmol/kg and presented the trend M-50BS/PA > M-50BS/CA > M-50BS/SD > M-50BS/ED > M-50BS > M. M-50BS remodified by 100% CEC of the composite modifier obtained superior Cu2+ adsorption, and the adsorption amount of Cu2+ was 1.10-1.20 times higher than that of M-BS remodified by 50% CEC of the composite modifier. (2) In the range of 20 degrees C to 40 degrees C, the adsorption amount of Cu2+ in the tested samples increased with the increase in temperature, except for M-50BS/PA and M-50BS/SD, and the increasing range was 7.56%-16.79%. (3) Within the pH range of 3 to 5, the Cu2+ adsorbed by each test sample increased with increasing pH value. The adsorption amount of Cu2+ on the tested maifanites (except M-50BS) decreased with increasing ionic strength, wherein the best amount was at 0.01 mol/L. (4) The adsorption of Cu2+ on the tested maifanites was a spontaneous, endothermic (except M-BS/PA and M-50BS/SD), and entropic-adding process.