Effective method of siliconization

UDC 669.184


EFFECTIVE METHOD OF SILICONIZATION
OF COPPER SLAGS OF ALMALYK MMC AND SYNTHESIS OF AMORPHOUS NANOPOWDERS SiO₂


М. Эрназаров¹, М.Ш. Курбанов², С.А. Тулаганов³, Ж.А. Панжиев^4*
Arifov Institute of Ion-Plasma and Laser Technologies of Uzbekistan Academy of Sciences
Dormon Road st, 100125, Tashkent city, Republic of Uzbekistan


Annotation
The article presents the results of the desiliconization of dump slags from the copper production of the Almalyk MMC by the fluoride method. The material balance of the separation of silicon dioxide from slags is given according to the proposed technology. It is presented that nanopowders of amorphous silicon dioxide can be synthesized from the technogenic waste of copper production, and the size distribution of their particles depends on the conditions of hydrolysis of ammonium hexafluorosilicate.


Key words: desiliconization, ammonium fluoride, slags, nanopowders, amorphous silicon dioxide, particle size, ammonium hexofluorosilicate.
At present, JSC "Almalyk MMC" has accumulated at least 15 million tons of dump slags from copper-smelting production, containing a lot of such valuable components as non-ferrous, noble and also rare metals, the extraction (or additional extraction) of which, from a technological point of view, is a rather difficult task. ... The chemical composition of these man-made wastes has a peculiarity in that they consist of 30 to 40% silicon dioxide SiO2. Therefore, removal of SiO2 from slags, i.e. desiliconizing them, allowing you to obtain a concentrate of the above valuable components. In addition, the implementation of an effective technology for the integrated processing of dump slags from copper-smelting production will also expand the raw material base of the republic's mining industry and improve the environmental situation.
The addition of SiO2 nanopowders makes it possible to improve and impart new properties to various materials. In particular, the addition of amorphous SiO2 nanoparticles increases durability, changes the viscosity and fluidity of paints, varnishes, adhesives and sealants [1, 2], and in the food industry, the addition of SiO2 nanopowders to food products prevents their clumping and sintering during heat treatment [3]. It is known the use of SiO2 nanopowders in the pharmaceutical industry [4], in the production of glass, abrasives, ceramics, as well as in the production of concrete as the main component [5], which increases its strength and other performance characteristics, and, finally, in electronics in the production of microcircuits and fiber -optical cables [6]. It should be noted that one of the important areas of application of amorphous SiO2 is the production of industrial rubber goods and plastics [7]. The addition of SiO2 as a reinforcing filler in a mixture for rubber production significantly increases the strength of products and, in comparison with carbon black, significantly reduces, for example, such a parameter as tire rolling resistance, which, in turn, leads to a decrease in vehicle fuel consumption [8].
The purpose of this work is to develop an effective technology for desiliconization of dump slags of copper smelting production in order to extract valuable components from them and control the synthesis of highly dispersed powders of amorphous silicon dioxide.
Table 1 (a) shows the results of chemical analysis of waste slag according to the passport data of JSC "Almalyk MMC" and according to the data of the Central Laboratory of the State Committee for Geology of the Republic of Uzbekistan (b).
Table 1 (a). Chemical composition of dump slags of JSC "Almalyk MMC", in%.

SiO2	Fe	Al2O3	Cu	CaO	S	Mg	Mo	Au, г/т	Ag, г/т
40,2	25,6	5,82	1,63	1,82	1,4	1,05	0,07	1,4	9,5

Table 1 (b). Chemical composition of dump slags of JSC "Almalyk MMC", in%.

SiO2	Fe2O3	FeO	TiO2	MnO	Al2O3	CaO	MgO	Na2O	K2O
29,8	12,2	41,4	0,23	0,2	4,17	2,58	1,3	0,22	1,43

As can be seen from the data in Table 1, the basis of the dump slag is silicon dioxide SiO2 and iron oxides, which together account for more than 80%. In the experiments, precisely these macrocomponents of the slag were initially removed to obtain the remaining valuable components in the remainder of the concentrate. To remove SiO2 from the slag, ammonium fluoride (or bifluoride) was used [9], and iron, after removing SiO2, was separated by magnetic separation [10]. A sieve analysis of crushed slags from the copper-smelting production of the Almalyk MMC was carried out, the results of which are presented in Table 2.

Table 2. Sieve analysis of crushed slag

Class, mm	Private	total
+ 20	3,6	10,6
-20 +16	7,0	48,2
-16 +12	37,0	54,3
-12 +10	6,1	72,3
-10 +6	18,0	87,0
-6 +2	14.7	92,2
-2 +0.59	5,2	94.48
-0,59 + 0,30	2.28	95,66
-0,30+ 0.21	1,18	97,21
-0.21 + 0,10	1,55	97,57
- 0,10 +0.071	0,36	100
- 0,071	2,43	total

The experimental setup is a furnace-reactor in the form of a cylinder with a diameter of 220 mm and a height of 520 mm and is equipped with thermoelements for heating the samples. It has three compartments; in the lower part of the installation there is a test sample (slag), previously homogenized with ammonium fluoride or bifluoride in a stoichiometric ratio to the content of silicon dioxide. The two upper parts are designed to collect ammonium hexafluorosilicate (NH4) 2SiF6, which is formed in the sublimation compartment from the sample base. The installation included a system of traps - condensers. The condenser for collecting (NH4) 2SiF6 is equipped with a special baffle to prevent the (NH4) 2SiF6 from falling into the starting material. The installation is also equipped with a system for capturing ammonia gas, which is formed during the reaction:

NH₄F + 6SiO₂ = (NH₄)₂SiF₆ + 4NH3 + 2H₂O (1)
A weighed portion of copper slag in the amount of 100 g, which passed the stage of charge preparation, was mixed with ammonium fluoride taken in a stoichiometric ratio with respect to SiO2 and placed in the lower segment of the installation intended for sublimation sublimation of (NH4) 2SiF6.
The temperature in the furnace was raised to 140 ° -150 ° C and held for 1 hour, then the temperature was brought to 350 ° -370 ° C and the samples were heat-treated for 1.5 hours. The temperature was measured with a thermocouple. After removing SiO2 from the slag base, iron was separated by magnetic separation. The remainder after processing was a collective concentrate containing such valuable components as copper, zinc, noble and light non-ferrous metals. Processing of concentrates for the recovery of these metals is carried out by standard pyro and hydrometallurgical methods.
For the regeneration of ammonium fluoride, the formed (NH4) 2SiF6 was placed in a flask and dissolved in a 10% ammonia solution with a 20% excess of the required stoichiometric amount according to the reaction:
(NH₄)₂SiF₆ + 4NH₄OH = 6NH₄F + SiO₂ + 2H₂O. (2)
The resulting mixture was stirred for 1 hour at room temperature, after which the precipitate was separated from the filtrate, washed three times and dried at 110 ° C. The result is a highly dispersed silicon oxide of high purity. The ammonium hexafluorosilicate wash solution had a blue tint, characteristic of copper compounds. Before evaporation, the solution was purified with a group precipitator (NH4) 2S.

Based on the data obtained, the material balance of desiliconization of the dump slag of the copper-smelting production was compiled, which is shown in Figure 1.

SiO-63,3 ,

Slag -100кг

NH4F-233,1 кг

Mixing

Opening oven

Sublimation of silicon

HFSA-184,0 кг

NH4ОН-964 кг

Treatment

NH4ОН

(NH4)2SiF6

Treatment

NH₄ОН

Filtration

H₂O-857,1 кг

Evaporation
NH4F

SiO₂

Drying 62,2кг

Finished product

SiO₂-62,2кг

NH4OH-190 кг

Filtration

34кг

solution

for cleaning

190,7кг

NH4F – 228,2 кг

NH3 – 52,42 кг

slag

Gases NH3

H2O

Capture

H2O-2кг



34,7 kg



NH4ОН



sediment

Sediment 68,2кг

Cyanidation



Calcination

Figure 1. Material balance according to the technological scheme of desiliconization of dump slag from copper smelting production by the fluoride method.

Table 3 shows the comparative results of the chemical compositions of the initial slag, slag after desiliconization and magnetic separation, i.e. collective concentrate obtained according to the proposed technological scheme for the processing of slags with ammonium fluoride.
Table 3. Chemical compositions of the initial slag, slag after magnetic separation and bulk concentrate, wt.%

Name	Si	Fe	Cu	Zn	Pb	Ni	S	Mo	K
Initial slag	40,0	27,0	1,6	0,96	0,44	0,03	1,4	0,07	0,7
After desiliconization	3,0	43,9	1,58	1,25	0,55	0,18	0,56	0.25	2.8
Collective concentrate	5,0	38,7	1,98	1,08	0,56	0,02	0,87	0,26	5,7

As can be seen from the data in Table 3, there is an increase in the content of valuable components in the processed product. Silicon dioxide is removed from the base by 75%. At the same time, the iron content in the final concentrate is 38.7%, and in the magnetic fraction - 43.9%. Such a high iron content in the final concentrate is apparently explained by its presence in the form of non-magnetic oxides.

Amorphous SiO2 separated from the solution was obtained in a nanosized dispersed state and has a purity of 99.96 wt%.
In fig. 2 shows the size distributions of the synthesized particles depending on the concentration of (NH4) 2SiF6 solutions obtained using a NanoSight LM10 laser analyzer (Malvern Panalytical).



Figure 2. Size distribution of synthesized amorphous SiO2 nanoparticles depending on the concentration of (NH4) 2SiF6 solutions: (A) -3% wt; (B) -10% of the mass; (C) -20 mass. % and (D) - 30% of the mass. concentration (NH4) 2SiF6. On the graphs, the shaded sections of the curves show the interval of changes in values for different measurements.
Figure 2 shows that the synthesized SiO2 powders have a fairly wide particle size distribution. Changing the conditions of hydrolysis of (NH4) 2SiF6 under the action of ammonia water, i.e. a change in its concentration in solution significantly affects the shape of the particle size distribution. The number of particles up to 100 nm in diameter at 3 wt% (NH4) 2SiF6 concentration in solution is only 4% (Fig. 2A), and at 20 wt% % - 23% (Fig. 2C) and at 30 wt. % - 35% (Figure 2D). An increase in the concentration of ammonium hexafluorosilicate during its hydrolization by a factor of 10 leads to a noticeable, up to 8-9 times, increase in the number of synthesized SiO2 particles having the smallest size (20-100 nm).
Thus, from the man-made waste of copper-smelting production using a fairly simple and economical method, at low fluorination temperatures and using one reagent - ammonium fluoride (bifluoride). can be synthesized highly dispersed powders of amorphous silicon dioxide, while most of the methods used for this require the use of high temperatures, a much larger set of reagents and a long technological process.
The results obtained can be recommended for use in various industries indicated at the beginning of the article, as well as in the creation of new nanocomposite materials and coatings, including polymeric ones, in the synthesis of which SiO2 nanopowders are used as fillers.