Tag Archives: Ion Exchange

Activation of Catalysts for Carbon Nanomaterial Production

The most important stage of preparing heterogeneous catalysts for carbon nanomaterial (CNM) is their activation, which is understood as a complex of physical influence on the catalytic material, which allows to significantly increase the efficiency of nanostructure synthesis.

This can be achieved by researching mechanical (dispersion) and physical (electromagnetic and ultrasonic) activation methods.

One of the most important factors defining catalyst efficiency is its granulometric composition. It is known that reduction of the particle size (less than 3 nanometers) causes capsulation inside nanotubes, while increasing it above 25 nanometers leads to uneven size distribution and defects in nanotubes. This is due to the fact the using large catalyst particles (25 to 100 nanometers) prevents carbon scattering from the surfaces where hydrocarbon decay occurs to the surfaces where carbon is deposited; as a consequence, no CNM growth occurs on such particles. Therefore, it is important to define reasonable catalyst particle size, as well as dispersion and classification methods.

Note that dispersion of catalyst microparticles causes both the reduction of size and the changes in the microstructure, e.g. destruction and reduction of pore depth, increasing the boundary of nano-seeds, where graphitized carbon is deposited.

Catalyst was activated in a drum mill and an electromagnetic vortex layer device (AVS). The distinguishing characteristic of the vortex layer in electromagnetic units is the multitude of high frequency and strength shocks, as well as friction, which not only break solid particles, but significantly activate their surfaces due to the deformation of their crystalline lattice. Enormous energy is concentrated in a volume of this process, which direct influence on the material. The influence is so high that it changes the structure as deeply as the atom’s valency shells. The process causes deep changes in the structure of the material.

Mean energy conducted to a volume of the vortex layer reaches 103 kW/m3. This is several orders of magnitude higher than in vibration mills, for instance. Besides, the energy is localized in certain areas, e.g. in the locations where the ferromagnetic particles collide, where mean power reaches even higher.

The electromagnetic vortex layer unit consisted of a process section and a control section, connected by oil tubes and a power cable. The process section consisted of a support, an enclosure, an induction coil for the rotating electromagnetic field, and a detachable operating chamber.

The catalyst activation process was performed with 1…1.5 mm by 10…15 mm PVC encapsulated ferromagnetic particles.

The chamber was loaded with 0.120 kg of the catalyst and 0.060 kg of ferromagnetic particles; retention time varied from 5 to 60 seconds. The granulometric composition of the Ni/MgO catalyst after the dispersion was done by fractionating sieve analysis. The catalyst after activation was separated into fractions and used for CNM synthesis under a unified method of testing various catalyst samples.

The results of the experiment show that the optimal duration time for the finest grinding constitutes 10 seconds, with initial catalyst particle size of 500 micron.

The observed increase of catalyst particle size after 10 or more seconds of dispersion is apparently due to the fact that with time the particles accumulate sufficient energy for spontaneous aggregation.

The analysis of the influence of the catalyst size composition on the mean output of CNM leads to the conclusion: the output increases in inverse proportion to catalyst particle size. This is due to the increased active surface of the catalyst. The experiments demonstrated that the actual method of catalyst dispersion has no significant influence on nanomaterial output.

Ion Exchange in Electroplating Wastewater Treatment

The process of ion exchange has found practical use in wastewater treatment and water preparation systems, specifically for demineralization, desalination, correction of the chemical composition of water, removal of toxic or valuable substances in processing natural or industrial wastewater.

Despite the abundance of the chemical properties of electroplating wastewater contaminants, both organic and inorganic, the specific chemical interaction of ions, which exchange ionites (forming complex functional groups, weakly ionized form of ionites) becomes important.

Ion exchange is the most environmentally dangerous technology for deep purification of water and using it as a part of combined water treatment systems requires research of the interconnected processes: the exchange of ions between phases and the transfer of solvent.

The end result of the balanced distribution in these system is the result of the Donnan distribution of components and the chemical reactions of ion exchange.

This can be explained by the structural changes in the system of ionite-solution, since we know that wastewater treatment begins with the cationic exchange of cation exchanger with a sulfate group. The sulfate group in this is an ionogenic group and has the highest affinity with multicharged ions, which are the primary contaminant in electroplating wastewater. This is due to the following processes:

  • strong electrostatic interaction of multicharged counter-ions with fixed ions;
  • strengthening of hydrogen bonds between the molecules of hydrate water;
  • strengthening of bonds with counter-ions and fixed ions.

Complete regeneration of cationite requires a 2.5 excess of acid, while desorption of double-charged ion from the cationite, even larger acid exceed is required. The result is that a significant excess of acid exists in wastewater after cationic exchange filters, along with the salts of copper, nickel, calcium etc. This limits the use of eluate (regeneration solutions) for their recycling.

The process of anionic exchange is performed consecutively first in low-basic and then in highly basic anion exchangers. The need to used low-basic anion exchangers is due to their easy regeneration, but the low-basic anion exchangers absorb practically no weak acids. It is important that highly basic anion exchangers function in any pH range. At the same time, highly basic anion exchangers are more difficult to regenerate.

At present, the degree of wastewater mineralization and reduction of its volume occurs. Therefore it is reasonable to consider combined batch or semi-batch systems with complete purification and final polishing to reuse the water in the production process.

Ion Exchange in Electroplating Wastewater Treatment Processes

The problem of contamination of water bodies with biogenic elements and protection of the environment is essential. The main source of contamination, which worsens water quality and disrupts ecosystems is the release of insufficiently treated wastewater.

Municipal treatment facilities, where biological treatment of water is performed through the traditional arrangement of aerotank and a secondary settling tank, cannot ensure high enough quality of the processed water to meet the requirements sufficient for release into water bodies, due to high concentrations of various forms of nitrogen and phosphorus.

The reasons of low efficiency of treatment plants are many: design flaws, obsolete technology, incorrect operation, water and contaminant composition different from anticipated due to the development of the industry.

The solution to the problem of pollution by inefficiently treated waste is to reconstruct most of the sewage facilities using advanced technology and new wastewater treatment developments. Most attention is now directed at processes, which can simultaneously remove phosphorus and nitrogen from wastewater. Considering the environmental factors, removal of nitrogen and phosphorus using biological denitrification and biological dephosphorization.

Removal of biogenic materials from wastewater can be done in several ways. All methods are divided into anaerobic, anoxic and aerobic.

Three areas must be created in aerotanks for biological denitrification and dephosphorization:

  • aerobic (high concentration of solved oxygen), with removal aerobic removal of organics, nitrification (biooxidation of ammonia nitrogen to nitrate nitrogen) and dephosphorization (rapid consumption of phosphates by bacteria);
  • anoxic (practically no solved oxygen, but nitrates and organics are present), with denitrification;
  • anaerobic (no solved oxygen, no nitrates and nitrites, organics present), with fermentation of organics to acetate, consumed by bacteria with formation of phosphates.

Anoxic and anaerobic conditions are created by changing aeration to mechanical agitation, although such reconstruction is costly for existing facilities. There is an alternative: to create anoxic conditions in the aerotank by low (the minimum required to prevent settling of biological sludge) intensity of aeration.

For existing aerotanks in traditional aerobic mode, implementation of biological denitrification and dephosphorization while keeping treatment capacity requires intensification of purification. Increasing the rate of aerobic process, including nitrification and biooxidation of organics, can reduce the volume of aerobic zone to allocate space in the tank for anoxic and anaerobic zones.