International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Here we present data on the preparation and adsorption properties of mixed zinc-calcium phosphates in aqueous dispersions. The phosphates were prepared by co-precipitation from aqueous solutions followed by autoclaving. The effects of various Ca/Zn initial molar ratios and the type of Ca- and Zn-precursor salts (chlorides and acetates) on the structure, morphology and adsorption properties of the obtained phosphates were investigated. Preliminary data on the adsorption of methylene blue indicated that the as obtained mixed zinccalcium phosphates are promising candidates for application as adsorbents.

Silica gels are one of the most widely used adsorbents. The best view of the properties of silicas as catalytic supports, adsorbents and other applications give the adsorption-texture parameters and especially the specific surface area. Hydrated silicon dioxide is amorphous (SiO2.nH2O),a reactive compound with various contains. Due to the serious practical interest of the determination of the specific surface area of materials many methods are developed and have found application. The study evaluates the impact of the surface and surface modification on the possibility of an express method for determination of specific surface areas of silica gels.

Among the various methods for water purification and treatment from contaminated industrial pollutants, one of the most used is the adsorption methods based on activated carbons. The purpose of our study is to investigate the correlation between the porous texture and chemical nature of the surface and sorption capacity of the activated carbon, obtained based on lignite coal. The object of the study is also to determine its effectiveness as a sorbent for Cd-ions purification of contaminated industrial water. The obtained data from the conducted investigation show that the adsorbent based on such kind of activated carbon has good qualities for water purification from various pollutants and heavy metals

The activated carbons are among the chemical products widely used in the industry and life. Thanks to their unique combination of adsorption and electric chemical properties related to their strongly developed specific surface, porous texture and chemical nature of the surface, they have not lost their attractiveness and application for more than 150 years. The use of various types of carbon adsorbents for solution discoloration, air deodorization, for medical and cosmetic purposes, has been known for centuries. Their appearance happens to be the natural development of one of the most ancient technologies – for obtaining wooden coals and is based on the increase of
the public consumption.

The study deals with preparation of carbon/SiO2 based natural composite material by slow pyrolysis of rice husks at 480° C. The phase composition, microstructure and morphology of the solid pyrolysis residue were investigated by XRD, FTIR spectrometry, thermal analysis, Hg-porosimetry, B.E.T. specific surface area and SEM-EDS. The sorption capacity of the pyrolyzed rice husks (PRH) upon adsorption of oil and oil products spills was determined. The obtained results revealed that PRH possess high sorption ability toward to gasoline, diesel, motor oil, light and heavy crude oil, in the range of 3.7 to 9.2 kg.kg-1. The adsorbent is characterized with hydrophobicity and buy-effect 90% more 10 days. PRH were investigated also as material for deep adsorption removal of thiophene from model fuel under batch mode. It was found that adsorption of 92% of the aromatic sulfur compound from the model fuel was achieved.

The main purpose of the study was to assess the usability of a new calculation algorithm for determining the surfactants effective diffusion coefficient. The adsorption of a mixture of non-ionic surfactants onto flat water-air interface was considered. Presented algorithm is composed of a two parts: Ward-Tordai equation solver based on Nyström method for integral equations and golden ratio optimization method used in inverse problem. In the investigation the Langmuir model of an isotherm was assumed. Presented algorithm was successfully used to determine the non-ionic surfactant – Nafol 810D (BRENNTAG) effective diffusion coefficient in the diffusion controlled adsorption process.

This article describes part of the results obtained during the development of a new generation of vaccine adjuvants based on nanostructured hydroxyphosphates of tunable composition and physicochemical characteristics. Colloidal gels of ferric hydroxyphosphates of various iron/phosphate ratios were prepared by precipitation techniques, sterilized by autoclaving and analyzed by transmission electron microscopy (TEM) and dark-field optical microscopy. The obtained materials were composed of a network of amorphous nanoparticles (<20 nm in size) that were aggregated into micron-sized structures in physiological saline. Preliminary adsorption experiments indicated the ability of the obtained materials to adsorb protein substances, which is an important prerequisite for their potential application as vaccine adjuvants and further optimization of the production process to achieve reproducibility of the physicochemical characteristics.

Possibility of using waste mold sand for removal of acetic acid from the aqueous solution was studied in this article. Green sand can be used several times in mold making. When the properties of green sand are not suitable for further use, it becomes waste. Waste mold sand was used in this article as an adsorbent for the removal of acetic acid from the aqueous solution. During the adsorption process, the influence of the amount of the adsorbent and contact time adsorbent/adsorbate (waste mold sand/acetic acid) on the capacity of the adsorption process was monitored. Amount of waste mold sand was varied from 25 to 125 g. Contact times were as follows: 15, 30 and 60 minutes. The obtained results indicate that the adsorption of acetic acid on the waste mold sand occurred at all used combinations of these parameters. However, for all used contact times, the greatest adsorption capacity is achieved when the ratio of waste mold sand/acetic acid was 25 g/100 mL. For all the used amount of adsorbent, the highest adsorption capacity, i.e. dynamic equilibrium was achieved very quickly, after 15 minutes. The obtained results are in accordance with the chemical composition of the waste mold sand.

This article presents the application of non-hazardous waste molding sand from gray cast iron foundry as an inexpensive adsorbent for removal of Zn(II) and Cu(II) ions from aqueous solutions. The experiments were performed at room temperature using a multi solution (Zn + Cu) with concentration was 100 mg/l. The process of removal of Zn(II) and Cu(II) ions was monitored at different contact times of waste molding sand and metal ions. The experimental data were processed by two different kinetic theories. The pseudo-first-order and pseudo- second-order models were used for modeling the kinetic rates.

Obtained results show that the waste molding sand has significant potential for the removal of Zn(II) and Cu(II) ions from aqueous solutions. Research shows that the removal of Cu(II) ions was better than removal of Zn (II) ions. It is possible to conclude that the mutual competition of Cu(II) and Zn(II) ions for adsorption sites affect the intensity of their removal.

The paper is a presentation of the monography “Chr. Boyadjiev, M. Doichinova, B. Boyadjiev, P. Popova-Krumova, Modeling of Column Apparatus Processes, Springer-Verlag, Berlin Heidelberg, 2016, pp. 313. A new approach to modeling the mass transfer processes in industrial column apparatuses, in the physical approximations of the mechanics of continua, is used for the creation of convection-diffusion and average-concentration models. The models of chemical, absorption, adsorption and catalytic processes are presented.