Biomedical subjects

Jordi Cama

Publications and source records attributed to Jordi Cama.

5 recordsLinked to original sources

PubMed2006

Use of caustic magnesia to remove cadmium, nickel, and cobalt from water in passive treatment systems: column experiments.

In the present study caustic magnesia obtained from calcination of magnesium carbonate was tested in column experiments as an alternative material for passive remediation systems to remove divalent metals. Caustic magnesia reacts with water to form magnesium hydroxide, which dissolves increasing the pH to values higher than 8.5. At these pH values, cadmium is precipitated as otavite and to a minor amount as a hydroxide. Cobalt and nickel are precipitated as hydroxides which form isostructural solids with brucite. Thus, metal concentrations as high as 75 mg/L in the inflowing water are depleted to values below 10 microg/L. Magnesia dissolution is sufficiently fast to treat flows as high as 0.5 m3/m2 x day. For reactive grain size of 2-4 mm, the column efficiency ends due to coating of the grains by precipitates, especially when iron and aluminum are present in the solution.

Cadmium↗

PubMed2005

Immobilization of heavy metals in polluted soils by the addition of zeolitic material synthesized from coal fly ash.

The use of zeolitic material synthesized from coal fly ash for the immobilization of pollutants in contaminated soils was investigated in experimental plots in the Guadiamar Valley (SW Spain). This area was affected by a pyrite slurry spill in April 1998. Although reclamation activities were completed in a few months, residual pyrite slurry mixed with soil accounted for relatively high leachable levels of trace elements such as Zn, Pb, As, Cu, Sb, Co, Tl and Cd. Phytoremediation strategies were adopted for the final recovery of the polluted soils. The immobilization of metals had previously been undertaken to avoid leaching processes and the consequent groundwater pollution. To this end, 1100 kg of high NaP1 (Na6[(AlO2)6(SiO2)10] .15H2O) zeolitic material was synthesized using fly ash from the Teruel power plant (NE Spain), in a 10 m3 reactor. This zeolitic material was manually applied using different doses (10000-25000 kg per hectare), into the 25 cm topsoil. Another plot (control) was maintained without zeolite. Sampling was carried out 1 and 2 years after the zeolite addition. The results show that the zeolitic material considerably decreases the leaching of Cd, Co, Cu, Ni, and Zn. The sorption of metals in soil clay minerals (illite) proved to be the main cause contributing to the immobilization of these pollutants. This sorption could be a consequence of the rise in pH from 3.3 to 7.6 owing to the alkalinity of the zeolitic material added (caused by traces of free lime in the fly ash, or residual NaOH from synthesis).

Carbon↗

PubMed2005

Dissolution kinetics of synthetic zeolite NaP1 and its implication to zeolite treatment of contaminated waters.

The effect of pH on the dissolution kinetics of NaP1 zeolite, which was produced from the alkaline treatment of coal fly ash and may be used for decontamination of acid mine waters, is studied. The sample contains considerable amounts of accessory phases that partly dissolve during the experiment. Therefore, the dissolution rate was estimated during a stage in which the Al/Si ratio was equal to that of NaP1 (0.6). The release rate of these elements is controlled by the dissolution of the zeolite itself during this stage. The dissolution rate of NaP1 slows down with increasing pH in the acidic range, becomes constant at an intermediate pH, and increases with increasing pH in the basic range. The observed changes in rates were described using a rate law based on a surface speciation model. Using this rate law, we calculated the half-life of NaP1 to be about 2 years at near neutral pH and less than 10 days at pH below 3. For the utilization of NaP1 in the treatment of wastewaters or acid mine waters, these short half-lives bear two implications: (1) The treated waters must be kept at near neutral pH, and NaP1 should be added periodically to the treated waters in order to compensate for zeolite loss. (2) In water treatment applications that require a relatively short reaction time, the zeolite removed from the effluents should be kept dry in order to avoid its decomposition and the consequent release of the adsorbed metal to the environment.

Carbon↗

PubMed2003

Surface protonation data of kaolinite-reevaluation based on dissolution experiments.

The aim of the present study is to compare available surface titration curves of kaolinite, to explain the differences between them, and to constrain their interpretation based on predictions of surface protonation that emerged from dissolution experiments. Comparison of six surface titration curves obtained at 25 degrees C reveals significant discrepancies, both in the shape of the curves and in the pH of the point of zero net proton charge (pH(PZNPC)). Based on an analysis of the different sites available for adsorption on kaolinite surfaces we conclude that different kaolinite samples are expected to have similar pH(PZNPC). Therefore, the major reason for the differences in the observed surface protonation is related to the different ways in which the pH(PZNPC) was determined. To compare the titration curves, some of the curves were recalculated so that the proton surface concentrations of all the titration curves would be zero around pH 5. As a result, we obtained a good agreement between the titration curves. A prediction of the molar fraction of protonated sites was retrieved from modeling of kaolinite dissolution reaction and was compared to the protonation data obtained from surface titration. The model successfully predicts the surface protonation data of most of the surface titrations.

Hydrogen-Ion Concentration↗

PubMed2003

Passive in situ remediation of metal-polluted water with caustic magnesia: evidence from column experiments.

Passive remediation consists of a permeable system that enables the water to pass through while retaining metals by means of biogeochemical reactions. Conventional passive treatments are based on calcite dissolution. This increases the pH to values between 6 and 7, which are insufficiently high to precipitate divalent metals. Alternative treatments are based on sulfate reduction with organic matter in order to precipitate metal sulfides. However, redox reactions are usually too slow to treat large groundwater flows as currently found in gravel aquifers (>50 m/a). Caustic magnesia obtained from calcination of magnesium carbonate was tested as an alternative material to devising passive remediation systems. Caustic magnesia reacts with water to form magnesium hydroxide, which dissolves, increasing the pH to values higher than 8.5. Then zinc and lead are mainly precipitated as hydroxides, copper is precipitated as hydroxysulfate, and manganese(II) is oxidized and precipitated as manganese(III) oxides. Thus, metal concentrations as high as 75 mg/L in the inflowing water are depleted to values below 0.04 mg/L. Magnesia dissolution is sufficiently fast to treat flows as high as 100 m/a. The new precipitates may lead to a permeability drop in the porous treating system. Mixtures of caustic magnesia and an inert material such as silica sand (approximately 50% of each) have been shown to be as reactive as pure magnesia and permeable for a longer time (more than 10 months and 1000 pore vol).

Antacids↗