The total annual production of agricultural biomass such as wood, corn cobs, leaves, and citrus peels, is estimated at 956 million tons (Mt). Since crop residues are by-products of agricultural production, crop residue collection does not compete with food crops for acreage and therefore, it does not negatively impact food prices. Moreover, it has the advantage of reducing the amount of waste, the disposal of which often becomes a serious problem despite natural sources. Biomass conversion becomes a very valid alternative to diversify energy sources and reduce global warming. Thermochemical treatment of biomass is a promising way to convert biomass into bio-oil, biochar, and gas. In recent years, interest in the conversion of plant biomass into biochar has increased because this carbonaceous material has interesting properties that guarantee applications in wastewater treatment, soil improvement, solid fuels, and energy. The processes performed to convert biomass into biochar are different and the most used are thermochemical processes: pyrolysis, torrefaction, hydrothermal treatment, and gasification. The studies of the thermokinetic parameters that control these processes are carried out using different methods that provide the necessary information for the applicability of the processes on an industrial scale. One of the objectives of the present review is to compare kinetic models in order to clarify the role of the conversion process and the effects of the process parameters on the final product. A comprehensive investigation of the thermokinetic parameters controlling the conversion of crop residues to biochar was conducted. The mathematical description of kinetic processes is usually performed using the Arrhenius equation and its derivatives to obtain the activation energies (E_a), the pre-exponential parameter, and the process mechanisms. While isothermal processes can be described using the model fitting method, isoconversional processes can be studied using both the model fitting method and model-free methods. The high complexity and diversity of the reactions involved could lead to the use of approximations. In this paper, an overview of the kinetic parameters determined for biochar production processes and the model used to determine them is given.

Nanoparticles are increasingly in demand in such rapidly developing types of human activity as microelectronics, catalysis, biosensors, etc. The mild neutralization process is desirable to obtain a high-quality product due to forming a great amount of nucleation centers. The advantage of carbamide application is its capability to dissolve in the reaction volume without interacting with it, and evenly distribute in volume, slowly hydrolyzing with ammonium ions formation. At the same time, a very mild neutralization regime is realized without local pH value excess. Method of iron oxyhydroxide obtaining by carbamide precipitation is illustrated below. The aim of investigation was to obtain nanoscale precipitate, to study the properties of the obtained material and to describe the precipitation process. The study of the iron (III) oxyhydroxide precipitation kinetics from the iron (III) sulphate solution, and a mathematical model of the process are presented in the article. A mathematical model of the precipitation process allows to take into account the influence of the substances concentration and the process temperature to the rate of precipitate production. The precipitate was characterized by X-ray and DTA analysis, as well as by Raman spectroscopy and scanning electron microscopy methods.

The given research is devoted to the development of the technology of utilization of lime-softening sludge to obtain calcium nitrate. Water treatment waste by chemical composition differs from natural raw materials such as limestone, which is traditionally used to obtain calcium nitrate. Sludge obtained at the stage of lime-softening contains about 70% calcium carbonate, a fairly large amount of iron, which enters the precipitate with solutions of coagulants, as well as organic impurities. Organic impurities come from river water and precipitate as a result of coagulation. The process of extracting calcium by the acid solution is stable. The results are well reproduced on two kinds of waste from different enterprises. This is explained both by the high dissolution rate of calcium carbonate in nitric acid, and the similar chemical composition of the waste. Not only calcium compounds, but also iron ones together with the organic component of liming sludge fall into the solution. A process scheme is proposed for cleaning the solution, which should include the stages of oxidation of the solution and subsequent precipitation of iron. The concentration of iron in the experimental solutions was up to 6 g/l. With the help of the calculations of the precipitate-solution equilibrium, it has been stated that iron in the area of low concentrations of nitric acid precipitates in the solution, and calcium stays in it. The decrease of the acid concentration was carried out by the addition of pure calcium carbonate. Kinetic studies of the process of iron precipitation on model solutions of iron (III) nitrate have been carried out. The second-order kinetic equation is obtained. The calculation of the process activation energy is available in the paper. The value of the energy is ~37 kJ/ mole, which is the evidence of the precipitation process in the transition area. The undissolved residue contains about 40% iron and can be used to obtain coagulants.Thus, the application of the proposed method will allow the best use of water treatment waste