Zeolite performance in removal of multicomponent heavy metal contamination from wastewater.

Efficient removal of heavy metal pollutants from wastewater by ion-exchange sorbents requires knowledge and understanding of the interplay between the adsorption patterns of the different components. The present study elucidates the simultaneous adsorption characteristics of six toxic heavy metal cations (Cd2+, Cr3+, Cu2+, Ni2+, Pb2+, and Zn2+) by two synthetic (13X and 4 A) and one natural (clinoptilolite) zeolite from solutions containing equimolar mixtures of the six metals. Equilibrium adsorption isotherms and equilibration dynamics were obtained by ICP-OES and complemented by EDXRF. An order of magnitude lower adsorption efficiency was exhibited by clinoptilolite (maximum of 0.12 mmol ions/g zeolite), relative to that obtained by the synthetic zeolites 13X and 4 A (a maximum of 2.9 and 1.65 mmol ions/g zeolite respectively). The strongest affinities to both zeolites were demonstrated by Pb2+ and Cr3+ (1.5 and 0.85 mmol/g zeolite respectively for 13X, and 0.8 and 0.4 mmol/g zeolite respectively for 4 A adsorbed from the highest solution concentration). The weakest affinities were observed by Cd2+ (0.1 mmol/g for both zeolites), Ni2+ (0.2 and 0.1 mmol/g for 13X and 4 A respectively), and Zn2+ (0.1 mmol/g for both zeolites). Large differences were observed between the two synthetic zeolites in terms of their equilibration dynamics and adsorption isotherms. Pronounced maxima were displayed in the adsorption isotherms for zeolites 13X and 4 A. The decline in adsorption of the weaker adsorbing ions with the increase in total solution concentration was attributed to the thermodynamic equilibrium between the ions adsorbed on the zeolite surface and those in the solution. Regeneration by 3 M KCL eluting solution resulted in considerable reduction in adsorption capacities following each desorption cycle.

Trace elements in cocoa solids and chocolate: an ICPMS study.

The concentrations of eight trace elements: lead (Pb), cadmium (Cd), chromium (Cr), manganese (Mn), cobalt (Co), arsenic (As), bismuth (Bi) and molybdenum (Mo), in chocolate, cocoa beans and products were studied by ICPMS. The study examined chocolate samples from different brands and countries with different concentrations of cocoa solids from each brand. The samples were digested and filtered to remove lipids and indium was used as an internal standard to correct matrix effects. A linear correlation was found between the level of several trace elements in chocolate and the cocoa solids content. Significant levels of Bi and As were found in the cocoa bean shells but not in the cocoa bean and chocolate. This may be attributed to environmental contamination. The presence of other elements was attributed to the manufacturing processes of cocoa and chocolate products. Children, who are big consumers of chocolates, may be at risk of exceeding the daily limit of lead; whereas one 10 g cube of dark chocolate may contain as much as 20% of the daily lead oral limit. Moreover chocolate may not be the only source of lead in their nutrition. For adults there is almost no risk of exceeding daily limits for trace metals ingestion because their digestive absorption of metals is very poor.

Precipitation of ammonium from concentrated industrial wastes as struvite: a search for the optimal reagents.

Precipitation of struvite (MgNH4PO4) is a known process for purification of wastewater from high concentrations of ammonium. The optimal conditions for precipitation are basic pH (around 9) and sufficient concentrations of magnesium and phosphate ions. In this work, we accomplished efficient precipitation of ammonium from concentrated industrial waste stream by using magnesium oxide (MgO) both as a source of magnesium ions and as a base. Best results were obtained with technical-grade MgO, which provided 99% removal of ammonium. Moreover, ammonium removal occurred already at pH 7, and the residual ammonium concentration (50 mg/L) remained constant upon addition of more MgO without rising again, as occurs with sodium hydroxide (NaOH). This process may have two other advantages; it also can be relevant for the problem of uncontrolled precipitation of struvite in the supernatant of anaerobic sludge treatment plants, and the precipitate can be used as a fertilizer.