M. Calero

Study of Cr (III) biosorption in a fixed-bed column

This research analyzes the potential use of the olive stone as a low-cost biosorbent for Cr (III) from aqueous solutions in a continuous system. First, experiments were carried out in fixed-bed column to test the influence of various parameters on breakthrough and saturation time. The breakthrough and saturation time increase with the decrease of the flow rate. The same effect is shown when the bed depth is increased. The olive stone sorption capacity, q(e), increases as the inlet Cr (III) concentration increases until a value close to 0.800 mg/g is reached, then q(e) remains constant. Column data obtained at different conditions were described using the Adams-Bohart, Thomas, Yoon and Nelson, and Dose-Response models. The breakthrough curve prediction by the Adams-Bohart and Dose-Response models were found to be very satisfactory. In particular, the Adams-Bohart model can be used to represent the initial region of breakthrough curve, whereas the Dose-Response model is the one which best reproduces the whole curve for all the inlet Cr (III) concentrations used. Finally, a study of pH evolution was carried out. The pH increases at the beginning, subsequently decreasing as time passes until practically reaching the initial value.

Chemical treatment of olive pomace : Effect on acid-basic properties and metal biosorption capacity

In this study, olive pomace, an agricultural waste that is very abundant in Mediterranean area, was modified by two chemical treatments in order to improve its biosorption capacity. Potentiometric titrations and IR analyses were used to characterise untreated olive pomace (OP), olive pomace treated by phosphoric acid (PAOP) and treated by hydrogen peroxide (HPOP). Acid-base properties of all investigated biosorbents were characterised by two main kinds of active sites, whose nature and concentration were determined by a mechanistic model assuming continuous distribution for the proton affinity constants. Titration modelling denoted that all investigated biosorbents (OP, PAOP and HPOP) were characterised by the same kinds of active sites (carboxylic and phenolic), but with different total concentrations with PAOP richer than OP and HPOP. Single metal equilibrium studies in batch reactors were carried out to determine the capacity of these sorbents for copper and cadmium ions at constant pH. Experimental data were analysed and compared using the Langmuir isotherm. The order of maximum uptake capacity of copper and cadmium ions on different biosorbents was PAOP>HPOP>OP. The maximum adsorption capacity of copper and cadmium, was obtained as 0.48 and 0.10 mmol/g, respectively, for PAOP. Metal biosorption tests in presence of Na(+) in solution were also carried out in order to evaluate the effect of chemical treatment on biomass selectivity. These data showed that PAOP is more selective for cadmium than the other sorbents, while similar selectivity was observed for copper.

Biosorption kinetics of Cd (II), Cr (III) and Pb (II) in aqueous solutions by olive stone.

A by-product from olive oil production, olive stone, was investigated for the removal of Cd (II), Cr (III) and Pb (II) from aqueous solutions. The kinetics of biosorption are studied, analyzing the effect of the initial concentration of metal and temperature. Pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models have been used to represent the kinetics of the process and obtain the main kinetic parameters. The results show that the pseudo-second order model is the one that best describes the biosorption of the three metal ions for all the range of experimental conditions investigated. For the three metal ions, the maximum biosoption capacity and the initial biosorption rate increase when the initial metal concentration rises. However, the kinetic constant decreases when the initial metal concentration increases. The temperature effect on biosorption capacity for Cd (II) and Cr (III) is less significant; however, for Pb (II) the effect of temperature is more important, especially when temperature rises from 25 to 40oC. The biosorption capacity at mmol/g of olive stone changes in the following order: Cr>Cd>Pb. Thus, for an initial concentration of 220 mg/l, a maximum sorption capacity of 0.079 mmol/g for Cr (III), 0.065 mmol/g for Cd (II) and 0.028 mmol/g for Pb (II) has been obtained.

Sorption of Cr (VI) onto Olive Stone in a Packed Bed Column: Prediction of Kinetic Parameters and Breakthrough Curves

This paper investigates the ability of olive stone to remove chromium (VI) ions from aqueous solution in a packed bed up-flow column with an internal diameter of 1.5 cm. The experiments were performed with a bed height of 15 g (13.4 cm) and a flow rate of 2 mL/min. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Adams-Bohart, Thomas, Yoon-Nelson, and Dose-Response models were applied to the experimental data. All models were found suitable for describing the whole or a definite part of the dynamic behavior of the column. The simulation of the whole breakthrough curve was effective with the Dose-Response model, but the initial part of the breakthrough was best predicted by the Adams-Bohart model. On the other hand, the results indicated that, at pH values of this work, approximately 50% of Cr (VI) is biosorbed by olive stone and the other 50% is reduced to Cr (III), both processes being of equal importance. Therefore, a two-stage biosorption process was developed. The goal of these final experiments was to confirm that Cr (III) [the Cr (VI) reduction product] was also effectively sorbed by olive stone in a second column.

Flotation of low-grade phosphate ore

A study has been conducted on the flotation concentration of sedimentary phosphorite from Sierra Espuna, in the province of Murcia (Spain), using a Denver D-12 mechanical subaeration cell. First, the mineral was pretreated through grinding, sorting and discarding slimes. The effect on flotation of pH, collector concentration, particle size and flotation time was then analyzed. The results achieved show that a neutral or slightly alkaline pH and short flotation times promote the concentration of sedimentary phosphorite.

Biosorption of Cr6+ from aqueous solution by sugarcane bagasse

AbstractThe biosorption characteristics of Cr6+ from aqueous solution using sugarcane bagasse (SCB) were investigated. Experimental parameters affecting the biosorption process, such as pH, contact time, initial metal concentration, and temperature were studied. The equilibrium nature of Cr6+ biosorption at different temperatures was described by the Freundlich, Langmuir, Sips, and Dubinin–Radushkevich isotherms. The biosorption isotherm of SCB for Cr6+ followed the Langmuir model, and the maximum biosorption capacity of Cr6+ obtained was 1.76 mg/g at 25°C. The biosorption kinetics of Cr6+ onto SCB followed the pseudo-second-order model. The calculated thermodynamic parameters (ΔG, ΔH, and ΔS) showed that the biosorption of Cr6+ ions were feasible, spontaneous (ΔG = −21.52 kJ·mol−1), and exothermic (ΔH = −6.364 kJ·mol−1) at the temperature range of 25–65°C.

Combustion of a Pb(II)-loaded olive tree pruning used as biosorbent

The olive tree pruning is a specific agroindustrial waste that can be successfully used as adsorbent, to remove Pb(II) from contaminated wastewater. Its final incineration has been studied in a thermobalance and in a laboratory flow reactor. The study aims at evaluating the fate of Pb during combustion, at two different scales of investigation. The flow reactor can treat samples approximately 10(2) larger than the conventional TGA. A detailed characterization of the raw and Pb(II)-loaded waste, before and after combustion is presented, including analysis of gas and solids products. The Pb(II)-loaded olive tree pruning has been prepared by a previous biosorption step in a lead solution, reaching a concentration of lead of 2.3 wt%. Several characterizations of the ashes and the mass balances proved that after the combustion, all the lead presents in the waste remained in ashes. Combustion in a flow reactor produced results consistent with those obtained in the thermobalance. It is thus confirmed that the combustion of Pb(II)-loaded olive tree pruning is a viable option to use it after the biosorption process. The Pb contained in the solid remained in the ashes, preventing possible environmental hazards.

Effect of the presence of chromium (III) on the removal of lead (II) from aqueous solutions by agricultural wastes.

The influence of the presence of Cr (III) on the biosorption of Pb (II) by three olive wastes (olive stone, the two-phase olive mill solid, and olive tree pruning) was investigated in a batch system in terms of equilibrium isotherm and adsorption yield. The results show that the three olive wastes have greater affinity for lead than for chromium and the best results are achieved at pH=5. The presence of chromium in the solution reduces the percentage of lead removal suggesting that there is a competition between the two metals for the binding sites, and that the biosorbent retains both species presenting more affinity for lead. Simultaneous biosorption phenomena of Pb (II) and Cr (III) on the three solid wastes were expressed by multicomponent isotherms. The extended Freundlich-type and Sips-type models were found to exhibit good fit to the experimental data for olive stone and olive tree pruning, respectively.

Kinetic considerations in the flotation of phosphate ore

Abstract A study was conducted on the flotation with oleic acid of sedimentary phosphates from Sierra Espuna, in the province of Murcia (Spain), also comprising an analysis of the kinetic considerations governing the operation. Two different flotation cells were used for this purpose, i.e. a Hallimond tube and a subaeration cell (Denver D-12). The results achieved with the Hallimond tube show that the rate of mineral flotation is medium to slow, while results with the Denver D-12 cell reveal a faster rate of flotation. It also became clear that the separation of the phosphate and calcareous fractions of the mineral (CaCO 3 ) is more intense at the very beginning of the operation. The flotation rate constants for mineral sizes between 160 and 325 ASTM mesh were determined, and a linear relationship between flotation rate constant and mineral sizes was shown to exist.

Comparative study of isotherm parameters of lead biosorption by two wastes of olive-oil production

Batch isotherm studies were carried out on a laboratory scale: (i) to investigate the effectiveness to remove lead of two wastes (olive stone (OS) and olive tree pruning (OTP)), untreated and chemically treated; and (ii) to examine the applicability of various adsorption isotherms to fit the experimental data. Results from tests were analyzed using seven equilibrium isotherm correlations (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Redlich-Peterson, Sips, and Toth equations). The sum of the squares of the errors was determined for each isotherm and the Langmuir equation provided the best fit. Chemical treatments increased the biosorption properties of these materials. The maximum biosorption capacities were: 6.33, 49.13, 14.83, and 38.93 mg g(-1) for untreated OS, HNO3-OS, H2SO4-OS, and NaOH-OS, respectively, and 26.72, 86.40, 72.78, and 123.80 mg g(-1) for untreated OTP, HNO3-OTP, H2SO4-OTP, and NaOH-OTP, respectively. Finally, the loss of mass for each waste (13.9, 14.3, and 36.8% for HNO3-OS, H2SO4-OS, and NaOH-OS and 35.1, 27.5, and 46.7% for HNO3-OTP, H2SO4-OTP, and NaOH-OTP, respectively) was taken into account and an effectiveness coefficient was determined for each adsorbent material.