Sánchez Rivera, Diana

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    Removal of cadmium, copper, and lead ions from aqueous solutions using waste crumb rubber as sorbent
    (2007) Sánchez Rivera, Diana; Román Velázquez, Félix R.; College of Arts and Sciencies - Sciences; Perales Pérez, Oscar; Vera, Marisol; Department of Chemistry; Rivera Santos, Jorge
    The removal of toxic heavy metals ions from aqueous solutions using waste tire crumb rubber (WTCR) as a low cost sorbent was studied. Nowadays, a variety of techniques exist to remove heavy metals from water such as, chemical precipitation, electrochemical techniques, and ionic exchange, among others. However, due to their high cost or low efficiency of removal at trace levels, adsorption is seen as a more cost efficient and realistic solution. In our study, parameters such as pH, metal concentration, competition with alkaline metals, and size of the sorbent used, were evaluated for each metal ion in order to optimize the sorption uptake conditions. In addition, mixtures of the metals and their desorption with nitric acid were also studied. The results showed that the metal uptake increased when the WTCR area exposed also increased. The equilibrium between the metal and WTCR surface is reached faster when the initial concentrations were lower (1, 5 ppm). The optimum pH for the three cations was pH 6.0. This is favorable because it is near the pH of most natural waters. Langmuir isotherms were constructed for each metal ion and the constant Qo, that represents the maximum sorbent capacity, was calculated. Lead was the better sorbed metal with a calculated Qo of 1.744 mg/g, followed by copper with a Langmuir constant value of 1.245 mg/g, and finally cadmium with a Qo value of 0.532 mg/g. The mechanism of sorption is facilitated by interactions with the oxygen groups present in the surface of carbon black, a main component of the rubber and ionic exchange with zinc.
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    Removal and speciation of oxyanions from aqueous solutions using Ca-Fe(III) alginate beads and dried sludge as adsorbents
    (2013) Sánchez Rivera, Diana; Román Velázquez, Félix R.; College of Arts and Sciences - Sciences; Meléndez, Enrique; Morell, Luis; Perales Pérez, Oscar J.; Department of Chemistry; Martínez Iñesta, María M.
    Oxyanions are highly soluble species, which are pH and redox dependant, and represent a toxic and hazardous species to humans and for the environment. Various remediation techniques have been applied such as: precipitation/coagulation, ultra filtration, bioremediation, and electrochemical techniques. These classical techniques usually have high energy consumption, high technical demand or poor removal efficiency especially at trace levels, where the oxyanions are still toxic. Instead, the adsorption processes are easy to scale up, affordable and highly efficient at trace levels. Adsorbents are widely available as commercial products or recyclable waste materials. This project describes a method to remove As(III), As(V), Se(IV), Se(VI), V(IV), and V(V) from aqueous solutions at trace levels concentrations using dried sludge and Ca-Fe(III) alginate beads. The sludge was obtained from the water filtration plant located in Miradero, Mayagüez, Puerto Rico. The sludge is a waste product discarded by the local Aqueduct and Sewage Authority, which increments the problem of waste disposal in Puerto Rican landfills. On the other hand, the Ca-alginate beads had been successfully applied for the removal of divalent cations. The insertion of iron as a dispersed colloidal ferric hydroxide in these alginate beads matrix enhances the corresponding adsorption toward oxyanions. The capacity to determine which oxyanion species are present is very important due to its varied toxicities, therefore speciation of the oxyanions species was performed using liquid chromatograph coupled with an inductively coupled plasma-mass spectrometer. The limit of detection (LOD) for the method are: As(III) 5.26 ppb, As(V) 9.85 ppb, Se(IV) 2.94 ppb, Se(VI) 3.10 ppb, V(IV) 2.31ppb and for V(V) 2.39 ppb. The developed method is fast, sensitive, and has multi-elemental capacity and uses no organic solvents; therefore, represents a green alternative to the environment. The adsorption isotherms were fitted by the Langmuir and the Freundlich models, being the last the more suitable. The Freundlich parameter k which is indicative of the relative uptake capacity of the adsorbent for the dried sludge system were: As(III) 0.221, As(V) 0.101, Se(IV) 0.100, Se(VI) 0.205, V(IV) 0.141 and for V(V) 0.832. The k Freundlich parameter for the Ca-Fe(III) alginate beads systems were: As(III) 0.122, As(V) 0.449, Se(IV) 0.407, Se(VI) 0.656, V(IV) 0.198 and for V(V) 0.899. Our results suggest that the main removal mechanism for vanadium and selenium species is due to a columbic attraction, forming primary outer-sphere complexes. Instead, for arsenic species, the main removal mechanism is due to the adsorption onto the iron in the alginate beads and sludge surfaces by forming primary inner-sphere complexes. Our results demonstrate that the dried sludge and Ca- Fe(III) alginate beads represent green alternatives to remove oxyanions at trace levels which can be used for water treatments.