Selenite Adsorption and Reduction via Iron(II) Impregnated Activated Carbon Produced from the Phosphoric Acid Activation of Construction Waste Wood.

Chemical activation of waste materials, to form activated carbon, (AC) is complicated by the large amounts of chemical activating agents required and wastewater produced. To address these problems, we have developed an optimized process for producing AC, by phosphoric acid activation of construction waste. Waste wood from construction sites was ground and treated with an optimized phosphoric acid digestion and activation that resulted in high surface areas (> 2000 m2/g) and a greater recovery of phosphoric acid. Subsequently the phosphoric acid activated carbon (PAC), was functionalized with iron salts and evaluated for its efficacy on the adsorption of selenite and selenate. Total phosphoric acid recovery was 96.7% for waste wood activated with 25% phosphoric acid at a 1:1 ratio, which is a substantially higher phosphoric acid recovery, than previous literature findings. Post activation impregnation of iron salts resulted in iron(II) species adsorbed to the PAC surface. The iron(II) chloride impregnated AC removed up to 11.41 ± 0.502 mg selenium per g Iron-PAC. Competitive ions such as sulfate and nitrate had little effect on selenium adsorption, however, phosphate concentration did negatively impact the selenium uptake at high phosphate levels. At 250 ppm, approximately 75% of adsorption capacity of both the selenate and the selenite solutions was lost, although selenium was still preferentially adsorbed. Peak adsorption occurred between a pH of 4 and 11, with a complete loss of adsorption at a pH of 13.

Metal-Impregnated Petroleum Coke-Derived Activated Carbon for the Adsorption of Arsenic in Acidic Waters.

The efficacy of metal-impregnated petroleum coke (PC) activated carbon for the adsorption of arsenite and arsenate in acidic waters is investigated in this study. Unmodified PC activated carbon, FeCl3-loaded activated carbon, KMnO4-loaded activated carbon, and a mixed FeCl3-KMnO4-loaded activated carbon were used for evaluation. The surface characteristics of the activated carbons before and after arsenic adsorption were analyzed by X-ray photoelectron spectroscopy (XPS). Arsenate adsorption was significantly improved by the addition of an iron-manganese-loaded activated carbon, increasing adsorption from 8.12 to 50.93%. Oxidation-reduction reactions are proposed based on the observed arsenic 2p3/2, iron 2p3/2, and manganese 2p3/2 XPS peaks. While iron in the iron-loaded activated carbon is not acting as the reducing agent, it is acting as a conductor for the flow of electrons from the activated carbon to the arsenic for reduction to take place prior to the physisorption of the arsenic. In the manganese-loaded activated carbon, manganese acts as the reducing agent for arsenic prior to arsenic adsorption to the surface through physisorption. XPS of the post-arsenic(V) exposure samples showed that the Fe2O3 species were reduced from 32.18 to 1.66% in the FeMn-loaded sample, while the FeOOH species were increased from 53.16 to 81.71%. Similarly, MnO in the FeMn-loaded activated carbon dropped from 26.82 to 15.40%, while MnOOH and MnO2 increased from 39.98 and 33.20 to 43.96 and 40.64%, respectively. This is consistent with the proposed mechanism. The adsorption of arsenite was also evaluated to show that the modification of the activated carbon adsorbed not only the arsenic(V) species but also the more toxic arsenic(III) species without the need for oxidation of the arsenic prior to adsorption.

Transforming micropores to mesopores by heat cycling KOH activated petcoke for improved kinetics of adsorption of naphthenic acids.

Formation of activated carbon from petroleum coke by KOH, results in high specific surface area materials that are predominantly microporous. This initial microporosity means that the adsorption kinetics of target species are not as rapid as they could be, thus limiting environmental remediation applications for the material. To address this problem a series of additional heat cycles with no additional chemical inputs were applied after activation but prior to the removal of activating agents. This process resulted in the oxidation of residual potassium metal from the initial activation which allows it to function again as an activating agent for the subsequent cycles. The heat cycling resulted in an increase in mesoporosity by 10-25% with each successive cycle independent of the KOH to feedstock ratio. This was shown to be demonstrably different than equivalently extended heating times, thus identifying the importance of thermal cycling. Adsorption kinetics of three model naphthenic acids showed faster kinetics for the pore widened activated carbon. The t1/2 times dropped from 20 to 6.6 min for diphenyl acetic acid, 34.3 to 4.5 min for cyclohexane acetic acid, and 51.4 to 12.0 min for heptanoic acid.

Adsorption of Chromium (VI) Using an Activated Carbon Derived from Petroleum Coke Feedstock.

This study aims to determine the main adsorption mechanism by which chromium (VI) is adsorbed onto the surface of a petroleum-coke sourced activated carbon, a feedstock not prevalent in current literature. The study also aims to produce an activated carbon adsorbent that is both cost-effective and efficient for the removal of chromium (VI) in neutral waters. The efficacy of thermally-treated petroleum coke-activated carbon and nitrogenated petroleum coke-activated carbon using ammonium chloride is compared to the efficacy of commercially available activated carbon. X-ray photoelectron spectroscopy of the activated carbons was obtained both before and after exposure to chromium (VI) for characterization of the materials and confirmation of chromium adsorption. The thermally-treated and nitrogenated activated carbons showed significant enhancement of chromium (VI) removal compared to the non-treated petroleum coke-activated carbon (22.4 mg/g, 21.9 mg/g, and 17.0 mg/g, respectively). However, there was no significant difference observed between the thermally-treated and nitrogenated materials. This indicates that the nitrogenation of the surface does not improve the adsorption capacity of the activated carbon, but rather the thermal treatment itself. X-ray photoelectron spectroscopy showed a significant increase in the alcohol functional groups on the surface of the activated carbon material as a result of the heat-treatment process; from 16.02 atomic percent in the non-treated activated carbon to 26.3 atomic percent in the thermally-treated activated carbon. The alcohol functional groups present on the surface allow for chromium (VI) to undergo reduction to chromium (III) under a similar mechanism to the well-known Jones Oxidation Reaction where the reduced chromium (III) species are then physisorbed to the surface of the activated carbon. XPS results are consistent with this as the chromium species present on the surface of the adsorbent is primarily Cr(OH)3 (85.6% in the standard AC and 82.5% in the thermally-treated AC). Pseudo-first-order and pseudo-second-order kinetic modeling of the adsorbents indicate that they follow a pseudo-second-order reaction where the rate-limiting step is the chemical sorption of the adsorbate itself.

The application of silicon sol-gel technology to forensic blood substitute development: Investigation of the spreading dynamics onto a paper surface.

This work investigates the spreading dynamics of three candidate sol-gel solutions, of ranging viscosities, surface tensions and densities, and compares them with water and two commercial blood substitute products. Droplets were created with different sizes (10 to75µL) and impact velocities (1.4 to 6.0m/s) to strike 176gsm cardstock. Over 2200 droplets were created using the six different fluids and their final dried stain diameter was measured. Droplet spread was plotted using the Scheller and Bousfield correlation and uses effective viscosity as a parameter for non-Newtonian fluids. Comparing the results to an expected whole human blood range validated the spread of the candidate FBS sol-gel material in passive drip bloodstain pattern simulation. These findings complement the practical application of the material as a safe substitute for demonstrating droplet spread under controlled conditions on hard paper surfaces.

The application of silicon sol-gel technology to forensic blood substitute development: Mimicking aspects of whole human blood rheology.

Solution-gelation chemistry has promising applications in forensic synthetic blood substitute development. This research offers a silicon-based sol-gel approach to creating stable materials that share similar rheological properties to that of whole human blood samples. Room temperature, high water content, silicon sol-gels were created using the organosilane precursors 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate along with various concentrations of filler and pigment. Shear-thinning non-Newtonian properties were observed within most formulations of the presented materials. The effects of colloidal concentration, temperature, age and filler addition on the viscosity of the sol-gels were investigated. SEM-EDS analysis was used to identify the behavior of the fillers within the film and support their inclusion for basic bloodstain pattern simulation. A final proposed candidate sol-gel was assessed using a previously reported passive drip simulation test on a hard, dry surface and passed. This works represents encouraging development in providing safe material alternatives to using whole human blood for forensic training and research.

An Impact Velocity Device Design for Blood Spatter Pattern Generation with Considerations for High-Speed Video Analysis.

A mechanical device that uses gravitational and spring compression forces to create spatter patterns of known impact velocities is presented and discussed. The custom-made device uses either two or four springs (k1 = 267.8 N/m, k2 = 535.5 N/m) in parallel to create seventeen reproducible impact velocities between 2.1 and 4.0 m/s. The impactor is held at several known spring extensions using an electromagnet. Trigger inputs to the high-speed video camera allow the user to control the magnet's release while capturing video footage simultaneously. A polycarbonate base is used to allow for simultaneous monitoring of the side and bottom views of the impact event. Twenty-four patterns were created across the impact velocity range and analyzed using HemoSpat. Area of origin estimations fell within an acceptable range (ΔXav = -5.5 ± 1.9 cm, ΔYav = -2.6 ± 2.8 cm, ΔZav = +5.5 ± 3.8 cm), supporting distribution analysis for the use in research or bloodstain pattern training. This work provides a framework for those interested in developing a robust impact device.