Green Cycle: Sulfate Sorption from Natural Water on Anionic Clay Compound Obtained from Industry Wastewater

Abstract

In this paper we are describing a green cycle process. The first step was a novel hydrotalcite-like compound (HTLC) synthesized by a co-precipitating method, under standard ambient temperature and pressure, using chemical industry wastewater rich in divalent and trivalent cations, activated by a thermal treatment and finally characterized by scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDS) and thermogravimetric analysis (TGA). The second step was a series of batch sorption tests performed with this activated HTLC and untreated underground sulfurous water from the state of Puebla, México. The HTLC calcined at 500˚C/3 h exhibited the best sorption ability for ions, demonstrated a decrease of the hardness and sulfate ions to below the regional legal standards for drinking water. Once inactive after being used in water treatment, the sorbed ions were removed by ion exchange in a carbonate-containing solution, resulting in an 80% recycling of the material which upon activation demonstrated a retained capacity for water treatment. This recyclability suggests the exciting possibility of this novel compound as an efficient "green" technology in water treatment processes.

How Does Competition between Anionic Pollutants Affect Adsorption onto Mg–Al Layered Double Hydroxide? Three Competition Schemes

“…In general, the inorganic anions adsorb onto Mg–Al–LDH–NO 3 to a lower extent than the three dyes do, with the maximum adsorption capacity, Δ a n max , being always smaller than the AEC of the adsorbent (see Table ). It is worth noting that the present results are in good agreement with those reported on the retention of SO 4 2– and CrO 4 2– anions by Mg–Al–LDH–CO 3 and Mg–Al–LDH–Cl. , On the contrary, maximum retention capacities of various Mg–Al–LDHs containing CO 3 2– and Cl – as interlayer anions toward HPO 4 2– ranging between 0.6 and 3.7 mequiv g –1 were published in the literature. − …”

“…All adsorption curves have a characteristic shape representing a very steep initial portion at low equilibrium concentrations and an adsorption plateau at higher values. In general, the inorganic anions adsorb onto Mg−Al−LDH−NO 3 to a lower extent than the three dyes do, with the maximum adsorption capacity, Δ a n max , being always smaller than the AEC of the adsorbent (see Table 1 anions by Mg−Al−LDH−CO 3 22 and Mg−Al−LDH−Cl. 23,24 On the contrary, maximum retention capacities of various Mg− Al−LDHs containing CO 3 2− and Cl − as interlayer anions toward HPO 4 2− ranging between 0.6 and 3.7 mequiv g −1 were published in the literature.…”