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To provide a tool to evaluate the economic and ecological feasibility of new and existing mining projects using a combination of environmental goals expressed in life cycle assessment (LCA) results with economic goals expressed within life cycle costing (LCC).

Sustainability is developing into a target for an increasing number of industries and governments. As a consequence focus has shifted from the production process to the entire life cycle. LCA is a tool that can help producers make better decisions concerning environmental protection, whereas the aim of LCC analysis is to create a cost‐effective model for environmental impact assessment.

Study of the influence of the environmental cost of projects should be based on long‐term analysis of environmental investment. Using the life cycle net present value (LCNPV) method it is possible to compare different investment options, and this method can be treated as a tool that can help producers to make better decisions pertaining to environmental protection.

Internalisation of external costs and valuation of environmental costs are the biggest problems for LCC calculations.

Mining producers can reasonably expect that implementation of LCA and LCC will lead to minimisation of environmental impact of their activities and to more effective environmental, cost and waste management. This means savings through reducing the amount of waste emissions and a decrease in fees and fines.

The use of the tools described in this paper will increase the efficiency of the decision‐making process, demonstrating the connection between activity and devastation of the environment.

This work seeks to present results of research which allowed the development of a technological system for the sodium chromate production process on the basis of a semi‐empirical equation.

The proposed technological method is based on determining the defined process parameters (independent variables) which allow the complicated process to be controlled using only a few parameters that determine the chromate charge composition

By using the equation it is possible to determine the composition of this charge, knowing only the results of analyses of the main component of the chromic ore (i.e. Cr₂O₃) and the values of coefficients X, a and b. In this way, the process parameters X, a and b can be adopted as independent control variables of the sodium chromate process.

The proposed method for the sodium chromate production process includes the substitution of natural chromic raw material with waste from different recycling types of chromic waste.

Using the control of sodium chromate production with chromic mud in‐process recycling, the system of process control presented has proved itself in industrial practice for over a year.

This paper aims to describe a solution for cyclonic flue dust recycling based on the example of ferrochromium producers in Kazakhstan. It includes environmental improvement, which can be assessed in detail based on LCA after the development of a feasibility study of such a proposal.

Three pyrometallurgical recycling approaches should be achieved. The first approach is reduction smelting of fine waste in a direct current arc furnace without preliminary agglomeration. The second is reduction smelting of agglomerated waste in a submerged arc furnace, and the third is processing of agglomerated waste with liquid cast iron. The last approach facilitates the reactions of metal oxide reduction by carbon and silicon from the iron with a corresponding decrease in energy and auxiliary material consumption.

Valuable material can be produced from ferrochromium dust waste using environmentally friendly technology, including electric furnaces that can operate in SAF regimes and a simple plasma high‐power DC reactor operating under a neutral or reducing atmosphere. Finally, the investigation of waste recycling has developed a novel approach that facilitates metal oxide reduction and provides low energy and auxiliary materials consumption.

Research into the treatment of flue dust generated in the ferrochromium industry is needed to solve environmental problems not only in Kazakhstan but also in all ferrochromium plants in the world.

The three proposed pyrometallurgical recycling approaches should be achieved on a large scale.

This paper sets out to observe the changes occurring during thermal processing of Na₂CO₃ and FePO₄ · 2H₂O in control trials, then analyses the influence on availability of phosphorus compounds in comparison with pure FePO₄ · 2H₂O.

Control trials of Na₂CO₃/FePO₄ · 2H₂O with molar ratios in the range 0.5‐5.0 were heated to a temperature of 850°C, then calcined within 3 hours without mixing. Cooled products were submitted for chemical analysis regarding the content of phosphorus soluble in cold water, 0.4 percent HCl, 2 percent citric acid and aqua regia as well as crystallographic identification.

The addition of Na₂CO₃ significantly increases the availability of phosphorus compounds from FePO₄ · 2H₂O. The total amount of phosphorus in control trials after the calcining process is soluble in cold water, citric acid and HCl. The molar ratios used affect the type of crystalline phase formation only in the case of a molar ratio near to 1.0. Near‐perfect phosphorus availability in hematite phase formation was observed.

These preliminary results confirm the necessity for further investigation of the addition of Na₂CO₃ into industrial sewage sludge before the calcining process. The results may allow for a decrease in energy use during the combustion process and may create the possibility of recovering phosphorus compounds from ash using only cold water instead of mineral acids during the extraction process.

This paper is a new source of information about phosphorus recovery from sewage sludge.

To determine the influence of alkali components (especially Ca compounds) on the hematite phase formation during thermal processing of sewage sludge and the observation of transformations proceeding at different ratios of Ca to FePO₄.

The model compositions were heated to temperatures of 600°C and 950°C, then calcined within 3 hours without mixing. Cooled products were subjected chemical analysis regarding the content of phosphorus that was soluble in cold water, 0.4 per cent HCl, 2 percent citric acid and aqua regia as well as crystallographic identification.

On calcining at 600°C, CaO reacts with FePO₄, forming hydroxylapatite. The hematite phase which is insoluble in mineral acids crystallizes above 600°C. Further increasing the calcining temperature leads to transformations resulting in Ca₉Fe(PO₄)₇ and hematite formation. Molar ratios of CaO to FePO₄ · 2H₂O of 1.0 and 2.0 lead to hematite phase formation and increase the availability of phosphorus compounds (characterized by phosphate solubility in 0.4 percent HCl and 2 percent citric acid) in compositions after calcining.

The addition of CaO to sewage sludge before the combustion process should be beneficial from the point of view of further extraction of phosphorus compounds from the ash obtained. Suitable CaO addition favours iron binding into the hematite phase and raises the solubility of the phosphorus compounds in the ashes formed.

This paper is a new source of information which complements existing knowledge about phosphorus recovery from sewage sludge.