Ammonium Fluorides in Mineral Processing

*Alexander Dyachenko*

### **Abstract**

The possibility of using ammonium fluoride as a new reagent for processing mineral raw materials is considered. Ammonium fluorides are the most convenient and technological fluorinating agents for the decomposition of the silicon component of ores. Advantages the use of ammonium fluoride (or hydrodifluoride) as a desiliconizing agent, the possibility of its complete regeneration. The processes of deep processing of silicon, zirconium, titanium, and beryllium minerals are considered. The excellence of using ammonium fluoride in the processing of mineral raw materials have been proven. The physicochemical laws of the processes are considered, technological schemes are proposed. The material will be useful in the further introduction of fluoride technologies at enterprises for the processing of quartz, zircon, ilmenite, and phenakite.

**Keywords:** mineral raw materials, ammonium fluoride, beryllium, zirconium, titanium dioxide, silicon dioxide

### **1. Introduction**

Hydrometallurgy of non-ferrous and rare metals with a high energy intensity of the release of microcomponents from mineral raw materials and a significant negative situation on the biosphere. These factors lead to the need to create fundamentally new technologies in which the amount of waste is minimized. In an ideal chemical technology, any waste should become a commercial product, and the reagents should undergo complete regeneration and return to production.

Currently, one valuable component is usually extracted from complex ores, the rest go into slag. The amount of waste in modern chemical plants is boggles the imagination.

The basis of mineral and technogenic raw materials is usually silicon oxide and iron oxides. The opening of the silica component is chemically difficult, and the removal of a large amount of the cheap iron component can make the entire processing of the material unprofitable. Silicate minerals interfere with the hydrometallurgical interaction of the recovered commercial component with the reagent. Pyrometallurgical technologies are energy consuming.

One of the promising technologies is the fluoroammonium technology for processing mineral raw materials.

This article is devoted to the technology of complex processing of natural mineral and technogenic raw materials using ammonium fluorides.

The difference in the properties of ammonium fluorometallates is the physicochemical basis of the decomposition of mineral raw materials using ammonium fluorides. Metal fluorides notably differ in their in boiling point. Some are volatile and evaporate or sublimate when heated, separating from the main mass. Other fluorides are soluble and can be leached out of the fluorinated mass. Some undergo pyrohydrolysis or have different precipitation pH. After fluorination in a molten ammonium fluoride, a mixture of fluorides and ammonium fluorometallates is obtained.

By varying the differences in the physicochemical properties of ammonium fluorides and fluorometallates, it is possible to select modes for the complete separation of the mineral mixture into individual components.

Ammonium fluoride NH4F under normal conditions is a non-aggressive, solid, and crystalline substance. Molten ammonium fluoride is an energetic fluorinating agent. Instead of ammonium fluoride, it is possible to use ammonium bifluoride NH4HF2. The melting point of NH4F is 126°C, the boiling point of NH4HF2 is 239°C. NH4HF2 vapors are mainly composed of HF and NH3. NH4HF2 is highly soluble in water, anhydrous HF, and hydrofluoric acid.

The interaction of most oxides with elemental fluorine, hydrogen fluoride, and hydrofluoric acid has been studied in sufficient detail [1]. The fluorination of mineral raw materials with ammonium fluorides requires further study. Silicon oxide is removed from the system in the form of volatile ammonium hexafluorosilicate at temperatures above 320°C.

Fluorination of metal oxides with fluoride and ammonium hydrodifluoride has been studied to a lesser extent. And the reactions of some fairly common oxides (Sn, Cu, Mn, and Ca), in order to create technological processes, have practically not been studied. The desiliconization cycle makes it possible to project similar processes of fluorination and regeneration of ammonium fluoride onto other oxides.

Regeneration is carried out due to the fact that oxides react well with molten ammonium fluorides at elevated temperatures, but do not react with ammonium fluoride solution in an alkaline medium.

### **2. Methodology**

Thermal analysis was performed using thermogravimetric analysis (DTA)—is the starting characterization test for any thermal analysis. This characterization test gives an understanding of the thermal stability of a sample by giving a weight loss/gain signal as the sample is heated at a known rate in time and exposure to a given atmosphere. Hydrofluorination of oxides in a molten ammonium fluoride was carried out using a TGA/DSC/DTA analyzer SDT Q600 with software processing of data from TA Universal V4.2E instruments. Sample weight: up to 200 mg. Thermocouples: Pt/Pt-Rh. Crucibles: platinum, volume 110 μl. The temperatures of the onset of the reaction, the formation, and decomposition of complex fluoroammonium salts were investigated by the DTA-methods [2].

Thermal analysis of the interaction of oxides with ammonium hydrodifluoride made it possible to determine the temperature ranges in which complex fluoroammonium complexes are formed and their thermal destruction to individual oxides occurs. SiO2, Al2O3, Fe2O3, and TiO2 form complex fluoroammonium

#### *Ammonium Fluorides in Mineral Processing DOI: http://dx.doi.org/10.5772/intechopen.101822*

compounds with ammonium fluorides—ammonium hexafluorometallates. NiO form ammonium tetrafluorometalate. CaO, CuO, and KOH—fluorinated to simple fluorides. Thermogravimetric analysis revealed the regularities of oxide fluorination, which are necessary for solving technological problems. The kinetic experiment made it possible to determine the activation energy and the reaction rate constant.

It is calculated that the thermodynamically optimal temperature for hydrofluorination of multicomponent silicate mixtures is 500 � 20 K. At a lower temperature, chemical reactions slow down. Increasing the temperature is not advisable, because decomposition of ammonium bifluoride into gaseous ammonia and hydrogen fluoride.

Based on DTA, the decomposition temperatures of fluoride compounds Al, Fe, Ni, Mn, Ca, and Cu, formed as a result of hydrofluorination in the melt of ammonium bifluoride, were found. The formation temperature of aluminum fluoride is 355°C, calcium fluoride 240°C, manganese fluoride 215°C, iron fluoride 365°C, nickel fluoride 295°C, and copper fluoride 260°C [3–5].

The kinetics of chemical reactions was investigated using the method of weighing the reacting mixture in the course of a chemical reaction. Weight loss occurs due to the formation of gaseous ammonia and water. The processing of experimental data was carried out according to the well-known methods of formal heterogeneous kinetics [6].

The possibility of separating multicomponent oxide silicate mixtures into individual oxides using only ammonium fluoride as an opening reagent has been experimentally proved.

Below are some specific examples of the application of ammonium fluoride technologies for the processing of mineral raw materials.
