Screening of variables affecting the selective leaching of valuable metals from waste motherboards' PCBs.

The presence of valuable and hazardous metals in waste printed circuit boards, especially, motherboards, makes their recovery necessary as implies great economic and environmental advantages and develops urban mining processes. Hence, this research is focused on the selective leaching of Cu, Pb, and Sn as base metals using nitric acid and hydrochloric acid and Au, Ag, and Pd as precious metals using thiourea and sodium thiosulfate from waste motherboards' PCBs in a sequential eco-friendly two-stage process. Previously, thiourea and sodium thiosulfate were used as leaching agents to investigate their applicability for the leaching of metals from PCBs in a single-stage process. Screening experimental design was applied to screen the variables affecting the leaching process in order to evaluate their impact on the recovery of metals and select the significant factors. The results demonstrated that base and precious metals can be leached appropriately in two consecutive stages compared to a single-stage process. Nitric acid was found to be a much more efficient agent to leach Cu and Pb in comparison with hydrochloric acid which was more suitable for the leaching of Sn. In the case of precious metals, higher amounts of Au were leached using thiourea, whereas sodium thiosulfate was able to leach more Pd. Roughly similar results were obtained for the leaching of Ag using these leaching agents. Nitric acid concentration, average particle size, temperature, and leaching time were found to be significant to maximize the leaching of Cu and Pb and minimize that for Au, Ag, and Pd in the first stage. Initial pH was the only variable influencing the second stage, in particular, Au leaching by thiourea.

S/N/O-Enriched Carbons from Polyacrylonitrile-Based Block Copolymers for Selective Separation of Gas Streams.

A series of polyacrylonitrile (PAN)-based block copolymers with poly(methyl methacrylate) (PMMA) as sacrificial bock were synthesized by atom transfer radical polymerization and used as precursors for the synthesis of porous carbons. The carbons enriched with O- and S-containing groups, introduced by controlled oxidation and sulfuration, respectively, were characterized by Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectrometry, and their surface textural properties were measured by a volumetric analyzer. We observed that the presence of sulfur tends to modify the structure of the carbons, from microporous to mesoporous, while the use of copolymers with a range of molar composition PAN/PMMA between 10/90 and 47/53 allows the obtainment of carbons with different degrees of porosity. The amount of sacrificial block only affects the morphology of carbons stabilized in oxygen, inducing their nanostructuration, but has no effect on their chemical composition. We also demonstrated their suitability for separating a typical N2/CO2 post-combustion stream.

Optimization of the Extraction of Bioactive Compounds from Walnut (Juglans major 209 x Juglans regia) Leaves: Antioxidant Capacity and Phenolic Profile.

This work studies the extraction of phenolic compounds from walnut leaves of the hybrid Juglans major 209 x Juglans regia based on extract antioxidant capacity. Once the solid/liquid ratio was selected (1/10 g/mL), by means of a Box-Benkhen experimental design, the influence of temperature (25-75 °C), time (30-120 min), and aqueous ethanol concentration (10-90%) on extraction yield and ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) antioxidant activities were analyzed. In all cases, the quadratic effect of % EtOH was the most significant, followed by the linear effect of temperature and, for most of the responses, the effect of time was almost negligible. Response surface analysis allowed to select the optimal extraction conditions: 75 °C, 120 min and 50% ethanol, which led to the following extract properties: extraction yield, 30.17%; FRAP, 1468 nmol ascorbic acid equivalents (AAE)/mg extract d.b.; DPPH, 1.318 mmol Trolox equivalents (TRE)/g extract d.b.; DPPH EC50, 0.11 mg/mL; ABTS, 1.256 mmol TRE/g extract (on dry basis) and ABTS EC50, 0.985 mg/mL. Quercetin 3-ß-D-glucoside, neochlorogenic acid, and chlorogenic acid, in this order, were the main compounds identified in this extract by ultra-performance liquid chromatography coupled with electrospray ionization and time-of-flight mass spectrometry (UPLC/ESI-QTOF-MS), with various potential applications that support this valorization alternative for walnut leaves.

Adsorption of an anionic dye (Congo red) from aqueous solutions by pine bark.

Pinus pinaster bark, an abundant by-product from the timber industry, has been studied as a potential low-cost adsorbent for the removal of Congo red (CR) dye from wastewaters. Surface morphological and physico-chemical characteristics of pine bark were analysed using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), determination of the point of zero charge (pHPZC) and elemental analysis. Assays were performed to determine the wavelength for the maximum absorbance and the stability with time of CR solutions depending on concentration and/or pH, which resulted to be a very significant parameter. Adsorption studies were conducted on batch mode to study the effect of contact time (till 7 days), pH (2-9), adsorbent dosage (1-10 g L-1) and temperature (25-60 °C). The bark adsorption capacity at equilibrium varied between 0.3 and 1.6 mg g-1 and the equilibrium adsorption percentage between 23.4 and 100% depending on adsorbent dosage, temperature and pH at an initial CR concentration of 5 mg L-1. Kinetic data for the removal of CR by pine bark were best fitted by the pseudo-second-order kinetic model. The equilibrium data fitted well with the Freundlich model. Thermodynamic analysis indicated that the adsorption process is exothermic and spontaneous.

Chestnut shell as heavy metal adsorbent: optimization study of lead, copper and zinc cations removal.

The influence of initial cation concentration, temperature and pH was investigated to optimize Pb(2+), Cu(2+) and Zn(2+) removal from aqueous solutions using acid formaldehyde pre-treated chestnut shell as adsorbent. Experiments were planned according to an incomplete 3(3) factorial experimental design. Under the optimal conditions selected, the metal ion adsorption equilibrium was satisfactorily described by the Langmuir isotherm model. The maximum pre-treated chestnut shell adsorption capacity was obtained for Pb(2+) ions, 8.5 mg g(-1), and the order of cation affinity was Pb(2+)>Cu(2+)>Zn(2+). A model that considered the effect of axial dispersion was successfully used to describe the fixed-bed adsorption behaviour of Pb(2+), Cu(2+) and Zn(2+) ions at the flow rates essayed. Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies showed that the functional groups involved in metal ions binding included carboxyl, hydroxyl, ether, alcoholic and amino groups.

Uptake of phenol from aqueous solutions by adsorption in a Pinus pinaster bark packed bed.

The adsorption of phenol from aqueous solutions using a column packed with pre-treated Pinus pinaster bark was studied. The influence of the inlet phenol concentration (0.01 or 0.1 g/L) and the flow rate (6, 15.6 or 30 mL/min) on the breakthrough curves was analysed. An increase in the flow rate, decreased the time necessary to reach the breakthrough point and, for the highest inlet concentration, the dynamic capacity of the bed, from 7.5 to 0.4 min and from 0.38 to 0.15 mg phenol/go.d. bark, respectively, at 0.1 g/L. The LUB Design Approach was used to determine the equivalent length of unused bed. The lower LUB values, which imply a better utilization of the bark bed, were obtained at the higher flow rate. A model which considered the effect of axial dispersion was successfully used to describe the fixed-bed operation behaviour for the lower flow rates. For the lowest inlet phenol concentration, the axial dispersion coefficient increased significantly when the flow rate increased.