Arsenic adsorption from aqueous solutions by activated red mud

Heat treatment and acid treatment methods have been tested on red mud to increase its arsenic adsorption capability. The results indicate that the adsorptive capacity of red mud can be increased by acid treatment. This treatment causes sodalite compounds to leach out. As(III) and As(V) adsorption characteristics of activated red mud have similar tendencies with raw red mud. Batch adsorption studies have shown that activated red mud in dosages ranging from 20 to 100 g l−1 can be used effectively to remove arsenic from aqueous solutions. The process is pH dependent, the optimum range being 5.8–7.5 for As(III) and 1.8–3.5 for As(V). The maximum removals are 96.52% for As(V) and 87.54% for As(III) for solutions with a final pH of 7.25 and 3.50, respectively, for the initial arsenic concentration of 133.5 μmol l−1 (10 mg l−1), activated red mud dosage of 20 g l−1, contact time of 60 min and temperature of 25 °C. The adsorption data obtained follow a first-order rate expression and fit the Langmuir isotherm well. Isotherms have been used to obtain the thermodynamic parameters. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic

Arsenic removal from aqueous solutions by adsorption on red mud

Use of red mud, which is a waste product from bauxite processing, has been explored as an alternate adsorbent for arsenic in this study. The tests showed that the alkaline aqueous medium (pH 9.5) favored the removal of As(III), whereas the pH range from 1.1 to 3.2 was effective for As(V) removal. The process of arsenic adsorption follows a first-order rate expression and obeys the Langmuir's model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. It would be advantageous to use this residue as an adsorbent replacing polyvalent metal salts

Preparation of cation exchanger from lemon and sorption of divalent heavy metals

A cation exchanging material was developed from lemon by modifying the pectic–cellulosic substances in the lemon peel by lemon juice having citric acid. For this purpose, chopped lemon removed from seeds and yellow skin was heated in two stages, firstly at 50 °C for 24 h and subsequently at 120 °C for 2 h. The material obtained was ground, repeatedly washed with water and dried. Lemon peel and lemon resin obtained were characterized through physicochemical analyses and FTIR spectroscopy. Heavy metal binding performance of this material was determined by removal tests conducted by using 10 mM solutions of divalent metals. Experimental results show that the resin prepared from lemon is effective especially for Pb and Cu removals. For a lemon resin dosage of 10 g l−1, sorption affinity of divalent metal ions is found to be in an order of Pb > Cu > Ni > Fe > Cd > Zn > Co > Mn. Typically, sorption capacities are about 0.87 and 0.43 mmol g−1 for Pb and Mn, respectively

Removal of phosphates from aqueous solutions by using bauxite: II.activation study

In this study, acid treatment and heat treatment methods have been investigated in order to enhance the phosphate adsorption capacity of bauxite. For this purpose, a series of bauxites treated with 0.1–1.0 M HCl and another one heated at various temperatures between 200 and 1000 °C were subjected to standardized orthophosphate adsorption tests. Besides determining chemical and mineralogical compositions, TGA and DTA were performed and point of zero net proton charge (PZNPC), surface area, mean particle size and porosity were measured for selected samples. The results have shown that the acid treatment of bauxite has a negative effect on the phosphate adsorption capability. On the other hand, it has been observed that the phosphate adsorption capacity of bauxite could be increased by heating. The optimum heating temperature was determined as 600 °C. Bauxite heated at 600 °C exhibited about an eight-fold increase in surface area compared with raw bauxite. The results showed that the activation of bauxite occurred via dehydration of boehmite and diaspore, being the hydrated mineral phases. Maximum adsorption efficiencies for ortho-, tripoly- and glycerophosphates were achieved in the slightly acidic pH range. It was found that the adsorption capacities of thermally-activated bauxite for all phosphate species investigated were higher than that of raw bauxite. But the increase in adsorption efficiency is not proportional to the increase in specific surface area. It was found that the relative adsorptivity of phosphate species investigated is in the order of orthophosphate > tripoly(phosphate) > glycerophosphate. In addition, it was found that the desorption trends of these phosphate species were similar to the results obtained for raw bauxite

Removal of phosphates from aqueous solutions by using bauxite: I. effect of pH on the adsorption of various phosphates

In this study, the effect of pH on adsorption of various forms of phosphate onto bauxite was investigated. For this purpose, the adsorption and desorption of inorganic (ortho and condensed) and organic phosphate species were studied. It was observed that the adsorption tendency of the various phosphate forms was different and depended on pH. Maximum adsorption efficiencies for all phosphate forms were achieved in slightly acidic conditions (pH 3.2–5.5). The results of adsorption and desorption studies showed that the adsorption of phosphates onto bauxite is based on a ligand exchange mechanism. The adsorption mechanism of inorganic condensed phosphates and organic phosphates is thought to be more complex than that of orthophosphate. It can be stated that the adsorption of organic phosphates is dependent on the functionality, number, and variety of organic groups. The results of experiments carried out with mixed phosphate solutions showed that the adsorption yields of various phosphate forms are dependent on the composition of the solution. The relative adsorptivity of various phosphates was found to be in the general order of hexametaphosphate > pyrophosphate > orthophosphate > tripolyphosphate > adenosine triphosphate > glycerophosphate > glucose-1-phosphate

As(V) removal from aqueous solutions by coagulation with liquid phase of red mud

As(V) removal by using liquid phase of red mud (LPRM) is reported in this article. The experimental section includes characterization of LPRM, as well as As(V) removal from arsenical aqueous solution mixed with LPRM by coagulation in the column. As(V) removal study was divided into two parts; neutralization of LPRM-arsenical solution mixtures with acid solution accompanied with air-agitation and neutralization of those mixtures with CO2 gas. Effect of LPRM/(As(V) solution) volumetric ratio on the removal of As(V) by co-precipitation arsenic together with aluminum present as aluminate in the LPRM were studied. Al/As(V) molar ratio values on the removal of As(V) is evaluated. Results show that As(V) was removed effectively by LPRM with a volumetric LPRM/(As(V) solution) ratio of 0.1 from an arsenical solution in the As(V) concentration of 20 mg dm−3. For an efficient removal, it was found to be required an Al/As(V) molar ratio of 6–8. The results suggest that it is advantageous to use a waste material of red mud liquid phase in the treatment of arsenical wastewater, possibly conjunction with red mud solids as adsorbent that its adsorption ability has been demonstrated earlier

Removal of hexavalent chromium by using heat-activated bauxite

In this study, to increase the Cr(VI) adsorption capacity of bauxite, heat treatment method was tested and the effects of pH, adsorbent dosage, contact time, initial Cr(VI) concentration and temperature on the adsorption of Cr(VI) were investigated. Although heating provides an enhanced adsorption, the heat-activated bauxite was found to be a weak adsorbent for Cr(VI). The maximum adsorption yield (64.9%) was obtained at the conditions of pH 2, activated bauxite dosage of 20 g l−1, contact time of 180 min, for the initial Cr(VI) concentration of 10 mg l−1 and temperature of 20 °C by using the bauxite sample heated at 600 °C. The adsorption data fit a first-order rate expression and Langmuir isotherm. Enthalpy, free energy and entropy changes were calculated from the isotherm data. The adsorption of Cr(VI) onto heat-activated bauxite was found to be exothermic

A study on the Cr(VI) removal from aqueous solutions by steel wool

The reduction of Cr(VI) by steel wool and the precipitation of reduced chromium by CaCO(3) powder and NaOH solution were investigated in continuous and batch systems, respectively. The effects of acid and initial Cr(VI) concentrations, volumetric rate and temperature of solution on Cr(VI) reduction were studied. The results showed that the reduction of Cr(VI), to a large extent, depended on, and increased with, acid concentration. The Cr(III) and iron ions in the reduced solution were completely precipitated by using NaOH solution at appropriate alkaline conditions. It was concluded that CaCO(3) powder could be used as a cheap precipitant for Cr(III) ions. But the iron ions in the reduced solution could not be fully removed by using this precipitant

Cr(VI) reduction in aqueous solutions by using copper smelter slag

The ability of Copper Smelter Slag (CSS) to reduce Cr(VI) in aqueous solutions has been investigated. The extent of reduction is dependent on the amounts of acid and reductant, contact time, Cr(VI) concentration, temperature of the solution and particle size of CSS. The amount of acid is the most important variable affecting the reduction process. When twice the amount of acid required with respect to Cr(VI) was used, Cr(VI) in 100 ml solution (100 mg/l) was completely reduced in a contact period less than 5 min by a 10 g/l dosage of CSS. Reduction efficiency increased with increase in temperature of solution, showing that the process is endothermic. Reduced chromium, and iron and other metals dissolved from CSS were effectively precipitated by using NaOH or calcinated carbonatation sludge from sugar plant

The removal of Cr(VI) from aqueous solutions using zinc extraction residue

This study deals with the removal of Cr(VI) from aqueous solutions by using filter cake known as zinc extraction residue (ZER) generated as a by product in a zinc production plant located in Kayseri-TURKEY. It was found that ZER, which is rich in lead compounds, has a great affinity for chromate ions. The Cr(VI) removal yield decreased with increasing initial concentration of Cr(VI) solution. An increase in the dosage of ZER caused an increase in the removal yield and the concentration of Pb, Cd and Zn released from ZER into the treated solution. The effect of temperature showed the removal process is endothermic. The removal process was highly pH dependent. 100 % removal of Cr(VI) was obtained at initial pH about 5.0 and 11.0 for the initial Cr(VI) concentration of 100 mg l−1 at 25 °C and 5 mg l−1 ZER dosage for contact time of 60 min. The removal percentage of Cr(VI) declined at pHs other than those mentioned above. Minimum removal (26.5 %) was observed at initial pH value of 3.05. XRD analysis showed that low-solubility lead chromates were formed in the removal process