Differences in adsorption mechanisms of heavy metal by two different plant biomasses: reed and brown seaweed.

The adsorption of Pb(II) by two different biomaterials, reed (Phragmites australis) and brown seaweed (Sargassum horneri) biomass pretreated with CaCl(2), were compared in an attempt to explain the differences in adsorption performance between the two biosorbents. A very interesting characteristic was found in their individual adsorption performances; the Pb(II) adsorption capacity of brown seaweed (Q(max)=0.45 mmol/g) was much higher than that of reed (Q(max)=0.05 mmol/g), but its adsorption affinity (b=112 L/mmol) was much lower compared with that of reed (b=471 L/mmol). To elucidate the mechanism, the elemental components, ion exchange phenomenon and roles of functional groups of these two biosorbents were compared. The higher Pb(II) adsorption by brown seaweed could be due to its richness in total functional groups and calcium contents on its surface. In contrast, the functional complexity, higher zeta potential and pK(a) value (deprotonation state) of reed are believed to lead to its high adsorption affinity.

Marine macroalga Sargassum horneri as biosorbent for heavy metal removal: roles of calcium in ion exchange mechanism.

Brown seaweed Sargassum horneri, a troublesome biomass scattered along the seashore, was utilized as a biosorbent for Pb(II) removal from aqueous solutions. The Pb(II) adsorption by brown seaweed was enhanced by pretreatment with CaCl(2), and the Langmuir adsorption isotherm equation showed a maximum capacity of a Q(max) of 0.696 mmol/g and a b value of 94.33 L/mmol. Results obtained from the mass-balance equation derived from the simulation model of the Langmuir adsorption isotherm suggested that the adsorption performance of brown seaweed biosorbent was sufficient to reduce the concentration of Pb(II) to meet the range of WHO guideline. The mechanism, as elucidated using pH monitoring, adsorption rate and ion exchange model, involved the rapid pH change of metal solutions that led to high reaction rate and Pb(II) uptake in the first 30 min of the biosorption process. The energy X-ray analysis's result confirmed the sharp reduction of calcium content in the biosorbent after Pb(II) adsorption. The amount of calcium ions released from the biosorbent was about 1.5 times the amount of Pb(II) adsorbed and proved the role of calcium in the ion exchange mechanism. These adsorption equilibrium and mechanistic studies provide useful information for system design and performance prediction of biosorption processes.

Pb(II) biosorption on reed biosorbent derived from wetland: effect of pretreatment on functional groups.

Reed biomass harvested from wetland constructed for water purification was modified into a biosorbent for Pb(ll) removal from aqueous solution. The enhancement of Pb(ll) adsorption by reed biosorbent depended not only on the types of reagent used for pretreatment, but also on the pH during the pretreatment process. The mechanisms, as elucidated using relational data obtained from Boehm titration, Fisher esterification and FTIR, involved the conversion of carboxylic groups into carboxylate groups, and proved the role of the carboxylate group, which occupied more than 80% in binding Pb(ll). The Langmuir sorption isotherm of Pb(ll) by R-NaOH-12 showed QO, and b values of 0.082 mmol/g and 312.5 g/mmol, suggesting enough adsorption performance to reduce the concentration of Pb(ll) to meet the range of WHO guidelines. The salinity of aqueous solution containing NaH2PO4 and NaN03 promoted the adsorption of Pb(ll), while NaCl and Na2SO4 suppressed the adsorption capacity of Pb(ll). The adsorption mechanism of reed biosorbent provides valuable insight on the pretreatment effects and the advantages of utilizing this plant as biosorbent for Pb(ll) and other heavy metals.