Novel Correlations between Spectroscopic and Morphological Properties of Activated Carbons from Waste Coffee Grounds

Massive quantities of spent coffee grounds (SCGs) are generated by users around the world. Different processes have been proposed for SCG valorization, including pyrolytic processes to achieve carbonaceous materials. Here, we report the preparation of activated carbons through pyrolytic processes carried out under different experimental conditions and in the presence of various porosity activators. Textural and chemical characterization of the obtained carbons have been achieved through Brunauer–Emmett–Teller (BET), ESEM, 13C solid state NMR, XPS, XRD, thermogravimetric and spectroscopic determinations. The aim of the paper is to relate these data to the preparation method, evaluating the correlation between the spectroscopic data and the physical and textural properties, also in comparison with the corresponding data obtained for three commercial activated carbons used in industrial adsorption processes. Some correlations have been observed between the Raman and XPS data

Activated Carbon from Spent Coffee Grounds: A Good Competitor of Commercial Carbons for Water Decontamination

In the framework of the circular economy, spent coffee grounds were converted into powdered activated carbon by means of pyrolysis, using potassium hydroxide as the activating agent. Its adsorption capacity on a panel of phenolic compounds was compared with those of two commercial powdered activated carbons, after preliminary studies on organic dyes with different ionic properties, to assess the affinity between adsorbates and adsorbents. Pseudo-first-order and pseudo-second-order kinetic models were carried out, together with Freundlich and Langmuir isotherms. They were useful to calculate the breakthrough at 5%, 10%, and 50% of adsorption and the partition coefficients for the comparison of performance between different sorbent systems in a less biased manner (e.g., reducing bias associated with operational settings like sorbate concentration and sorbents dosage). The results showed that the removal efficiency for SCGs-AC was comparable with that of the commercial activated carbons with the highest partition coefficients for methylene blue (12,455 mg/g/μM, adsorption capacity = 179 mg/g) and 3-chlorophenol (81.53 mg/g/μM, adsorption capacity = 3765 mg/g). The lower efficiency in bromothymol blue and bisphenol-A adsorption was due to its different morphology and surface properties

Production of Porous Ceramic Materials from Spent Fluorescent Lamps

Spent fluorescent lamps (SFL) are classified as hazardous materials in the European Waste Catalogue, which includes residues from various hi-tech devices. The most common end-of-life treatment of SFL consists in the recovery of rare earth elements from the phosphor powders, with associated problems in the management of the glass residues, which are usually landfilled. This study involves the manufacturing of porous ceramics from both the coarse glass-rich fraction and the phosphor-enriched fraction of spent fluorescent lamps. These porous materials, realizing the immobilization of Rare Earth Elements (REEs) within a glass matrix, are suggested for application in buildings as thermal and acoustic insulators. The proposed process is characterized by: (i) alkaline activation (2.5 M or 1 M NaOH aqueous solution); (ii) pre-curing at 75 °C; (iii) the addition of a surfactant (Triton X-100) for foaming at high-speed stirring; (iv) curing at 45 °C; (v) viscous flow sintering at 700 °C. All the final porous ceramics present a limited metal leaching and, in particular, the coarse glass fraction activated with 2.5 M NaOH solution leads to materials comparable to commercial glass foams in terms of mechanical properties

Bioliquids from raw waste animal fats: an alternative renewable energy source

Three different waste animal fats (bone, chicken, and tallow) have been studied to evaluate whether they could be used as bioliquids according to the European Regulation (EC) No.1069/2009. The analyses showed that they contained an unsuitable amount of free fatty acids (FFA) and impurities content (total sediment) if compared with the standards for power generation (set by UNI 6579:2009), with the exception of tallow fat (class C, UNI/TS 11163:2018). A series of physical-chemical processes already applied at industrial scale have been considered to manage the acid value and the impurities content. The FFA esterification was carried out with methanol, comparing two acid catalysts (sulfuric acid or Amberlyst \u2013 15), followed by neutralization of the residual acidity with two different bases (ammonia solution or solid sodium carbonate monohydrate) when necessary. The final purification has been achieved by treatment with powdered activated carbon. In particular, the bone fat was studied as reference material, having the worst initial physical-chemical characteristics. The UNI/TS 11163:2018 standard would allow to classify the bioliquid from bone fat belonging to class B, while the one from chicken would require further degumming and purification processes to reduce the metals, sulfur, and phosphorus content

Spent coffee grounds as a green source of highly active carbon sorbents

The coffee production amounted to approximately 159 million of 60 kg bags worldwide in 2012-2013, with the consequent formation of a similar quantity of residues and waste during the whole material life cycle, from the harvesting to the brewing. Furthermore, the consumption demand is increasing year by year. According with the directive 2008/98/EC, the waste production should be minimized through reuse and recycle, reducing the burden of waste management and disposal. This approach is useful to gain a circular economy and it could be improved by political incentives and by increasing the economic value of the waste. Based on these perspectives, the research project is focused on the conversion of spent coffee grounds, coming from different brands, into highly active porous sorbents by mean of pyrolysis. The treatment process was tested at different experimental conditions to obtain the best yield in terms of BET and adsorption capacity. Moreover, the pyrolysis was performed changing one parameter time by time, in order to understand the influence in the process of the temperature, the typology of inert and the related flow rate, the reagents’ dosage and the holding time. The initial coffee mass and the temperature ramp (10 °C/min) were kept constant for each experiment. At the end of the thermal treatment, each sample was washed with the same amount of deionized water until neutral pH and dried in oven at 105 °C. The obtained activated carbon was characterized by different microscopy and spectrophotometric techniques (i.e. ESEM, Raman, XRD, XPS, solid 13C NMR) together with the BET analysis, with the purpose to determine its physical and chemical nature. Finally, the adsorption capacity of each sample was evaluated for different pigments: methylene blue (cationic), erythrosine-b (anionic) and bromothymol blue (non-ionic). Their initial concentration and the amount of activated carbon used in the test were arbitrarily set. A fixed volume of pigments’ solution (100 ml) underwent adsorption and the concentration changing in time was evaluated with a UV-VIS spectrophotometer. Two different commercial activated carbons were analyzed as reference. They are commonly used for the treatment of potable water and wastewater, in particular for the removal of mobile persistent organic contaminants