Natural as well as acid modified dead biomass of brown marine alga Sargassum sp. was employed for the elimination of cadmium and zinc ions from synthetic wastewater; batch mode experiments were carried out to optimize various factors like adsorbent dosage, contact time, pH, agitation speed and primary metal ions concentration at room temperature (298.15 K) for both types of adsorbents i.e. natural and acid treated. Application of Langmuir and Freundlich isotherms suggested that the modified biomass adsorbed better as compared to the natural one; though sorption on the natural biomass was a physical process while that on the modified one was a physico-chemical process and thus was relatively difficult. The quantity of cadmium ions adsorbed was greater than that of zinc ions. Adsorption equilibrium for the metal ions sorption on treated Sargassum sp. biomass was established within 60 min for both cadmium and zinc ions with 95.3 and 90.1% removal efficiencies, respectively, but it was greatly influenced by the pH of the solution. The optimal conditions in the batch experiments were as follows: cadmium ions were removed effectively using 0.5 g of adsorbent and 5 mg/L initial metal ions concentration at pH 4 and 150 rpm agitation speed whereas the best results for zinc ions were obtained with 1 g of adsorbent and 5 mg/L initial metal ions concentration at pH 3 and 200 rpm agitation speed. The experimental data fitted well to the pseudo first order model as the values of metal uptake capacities were in good agreement with the experimental values. Thermodynamic studies show that the process is spontaneous and endothermic in nature. Desorption and regeneration studies reveal that recovery of biosorbent is low.
Lignite and lignite humic acids, which are used as soil amendments sometimes, are supposed to improve soil\ud
properties such as water holding capacity. The structure of those materials is composed of various organic molecules\ud
stabilized mostly byweak interactions. Therefore, excess ofwater causes only partial swelling, but most of\ud
the physical structure is destabilized. This accelerates the desiccation and hampers their application as natural\ud
hydrogel-like substances. In order to stabilize the structure of lignite humic acids and improve the water holding\ud
capacity, we applied formaldehyde cross-linking procedure based on covalent coupling of aromatic humic acids\ud
moieties. By combining the 1H NMR relaxometry and methods of thermal analysis, the kinetics and degree of hydration,\ud
water distribution and moisture uptake were investigated. It was found that cross-linking induced a reduction\ud
in moisture sorption capacity at lowrelative humidity and an increase at higher relative humidity,which\ud
was attributed to the separation of functional groups and decreasing of structural compactness after crosslinking.\ud
As a result, the cross-linked humic acids, exhibited faster water uptake and approximately three-fold\ud
higher water holding capacity in comparison with the parental sample. The distribution of relaxation times of\ud
water protons in swollen humic acids revealed the unification of pore size distribution upon cross-linking. Although\ud
the improved hydration of cross-linked lignite humic acids already resembles the hydration of some hydrophilic\ud
polymers, the water holding capacity is still belowthe capacity of classical hydrogels. Nevertheless, the\ud
lowprice of lignite, sorption properties and its overall positive affect on soil quality and productivity give a promise\ud
in application of this material both in agriculture and remediation technologies
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