Recuperação de metais com elevado valor comercial através da adsorção por carbonizados provenientes de resíduos da cultura do arroz Rice2Metal

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Activated carbons from the co-pyrolysis of rice wastes for Cr(III) removal

Publication . Dias, Diogo; Bernardo, Maria; Lapa, Nuno; Pinto, Filomena; Matos, Inês; Fonseca, Isabel Maria

ABSTRACT: Rice husk and polyethylene were mixed (50 % w/w each) and submitted to a pyrolysis assay. Four physical activations with CO2 were performed on the resulting co-pyrolysis char (PC). The activation at 800 °C, for 4h, generated the activated carbon (PAC3) with the best textural properties. PC, PAC3 and a commercial activated carbon (CAC) were characterized and submitted to Cr(III) removal assays. PC had a high percentage of volatile matter that was removed after the physical activation, resulting in more available pores in the final material (PAC). In the Cr(III) removal assays, two S/L ratios were tested: 5 and 10 g L-1. PC did not remove any Cr(III) from the solutions, but PAC presented similar results to CAC. At the S/L of 5 g L-1, Cr(III) removal was of 58.5 % for PAC and 62.5 % for CAC, both by adsorption mechanism; at the S/L of 10 g L-1, Cr(III) removal was almost complete due to precipitation caused by pH increase. The highest uptake capacities were of 7.92 mg g-1 for PAC and 8.71 mg g-1 for CAC, at the S/L of 5 g L-1. The results indicated that PAC3 may be a viable alternative to CAC on Cr(III) removal from aqueous media.

2018Journal article

Open access

Cr(III) removal from synthetic and industrial wastewaters by using co-gasification chars of rice waste streams

Publication . Dias, Diogo; Lapa, Nuno; Bernardo, Maria; Ribeiro, W.; Matos, Inês; Fonseca, Isabel Maria; Pinto, Filomena

ABSTRACT: Blends of rice waste streams were submitted to co-gasification assays. The resulting chars (G1C and G2C) were characterized and used in Cr(III) removal assays from a synthetic solution. A Commercial Activated Carbon (CAC) was used for comparison purposes. The chars were non-porous materials mainly composed by ashes (68.3-92.6% w/w). The influences of adsorbent loading (solid/liquid ratio - S/L) and initial pH in Cr(III) removal were tested. G2C at a S/L of 5 mg L-1 and an initial pH of 4.50 presented an uptake capacity significantly higher than CAC (7.29 and 2.59 mg g(-1), respectively). G2C was used in Cr(III) removal assays from an industrial wastewater with Cr(III) concentrations of 50, 100 and 200 mg L-1. Cr(III) removal by precipitation (uptake capacity ranging from 11.1 to 14.9mg g(-1)) was more effective in G2C, while adsorption (uptake capacity of 16.1 mg g(-1)) was the main removal mechanism in CAC.

2018Journal article

Open access

Cr(III) dynamic removal in a fixed-bed column by using a co-gasification char

Publication . Dias, Diogo; Bernardo, Maria; Pinto, Filomena; Fonseca, Isabel Maria; Lapa, Nuno

ABSTRACT: A char (GC) obtained from the co-gasification of rice husk and polyethylene was used in a fixed-bed column with continuous flow for Cr(III) removal assays from synthetic and industrial wastewaters. For comparison purposes, a commercial activated carbon (CAC) was also used. The best experimental conditions in the continuous removal assays were the following ones: Cr(III) inflow concentration = 5 mg L-1, feed flow rate = 3 mL min(-1), mass of adsorbent in the column = 0.8 g, and inflow temperature = 50 degrees C. Under these conditions, the highest uptake capacities were 1.60 and 2.14 mg g(-1) in the synthetic solution, and 3.25 and 7.83 mg g(-1) in the industrial wastewater, for GC and CAC, respectively. These results are different from those obtained under batch conditions in which GC performed better than CAC. Cr(III) removal by both adsorbents occurred due to precipitation, but CAC presented a slightly higher amount of Cr(III) removed due to its highest porosity. The regeneration of GC and CAC was also studied, but both adsorbents showed no capacity to be used in more than one cycle. This study highlighted the importance of studying Cr(III) removal under continuous conditions, as the removal mechanisms may be completely different from the batch assays, affecting the adsorbents' performance.

2021-10Journal article

Open access

Highly efficient porous carbons for the removal of W(VI) oxyanion from wastewaters

Publication . Dias, Diogo; Don, Davide; Jandosov, Jakpar; Bernardo, Maria; Pinto, Filomena; Fonseca, Isabel Maria; Sanches, André; Caetano, P. S.; Lyubchyk, Svitlana; Lapa, Nuno

ABSTRACT: Pyrolysis chars derived from rice wastes were chemically activated and used in W(VI) oxyanion adsorption assays in synthetic and mining wastewaters. For comparison purposes, a commercial activated carbon (CAC) was also used. Different experimental conditions were tested in the adsorption assays: solid/liquid ratio (S/L), initial pH, contact time, and initial W concentration. The porous carbon P2C+KOH presented the overall best performance in both media, due to its high surface area (2610 m2 g-1), mesopore volume (1.14 cm3 g-1), and neutral pHpzc (6.92). In the synthetic wastewater, the highest uptake capacity of P2C+KOH (854 mg g-1) was found in the assays with an S/L 0.1 g L-1, an initial pH 2, and an initial W concentration of 150 mg L-1, for 24 h. This value was almost 8 times higher than the one obtained for CAC (113 mg g-1). In the mining wastewater, P2C+KOH showed an even higher uptake capacity (1561 mg g-1) in the assay with the same experimental conditions, which was almost 3 times higher than for CAC (561 mg g-1). These results suggest that P2C+KOH seems to be an efficient alternative to CAC in the W(VI) adsorption from liquid effluents.

2021-06Journal article

Open access