SE444579B - PROCEDURE FOR THE TREATMENT OF METALLIC SUBSTANCE AND WASTE FROM THE METALLURGICAL INDUSTRY - Google Patents

Description

7902955-9 2 ïV “fl>" '?> ~ = ~ - s P ~ _. ._. Ss L liikttttiat woolen savalsepaiat which together with other dry mctallhaltiqä waste from the steel factory is fed llusbageugnen or AOD converter. Furthermore, the oil contained in the abrasive wool can also be extracted and the wool as such is added to the melt.

The inconveniences caused by abrasive wool with regard to the environment are most likely caused by the oil that can be released into the environment in connection with the wool's storage.

In addition, in the stainless steel industry, various types of oxide waste are generated, such as ball blasting dust, which are inert and do not normally cause environmental nuisance.

In order to utilize the waste, there are a number of methods in which the waste is reduced in an electric or a drum furnace, the dust and grinding wool generally either as such or pelleted and the moist precipitates in the dried state. The disadvantages of the methods are occupational hygiene and environmental problems caused by the dusting, whereby the hexavalent chromium plays a major role, due to the large investment and operating costs and the fact that these methods cannot treat all different types of waste at the same time.

In the process according to the invention, all wastes are dissolved in water or a pickling acid slurry, the pH of the slurry is raised if necessary to above 7 in order to precipitate heavy metals in the solution, after which water is removed from the solution, for example with a filter press, so that a final result is obtained. in unit form, which can be safely taken to the disposal site or stored for a desired period of time and for any further treatment for the recovery of valuable metals in the waste. By means of this procedure, all waste can be treated together. It also does not cause any occupational hygiene or environmental problems, since dusting problems do not arise and the hexavalent chromium is reduced in the process to three-valued.

The advantages also consist of low investment and operating costs and a remarkably high recycling of the metals. The zinc and lead can also be collected separately and removed from the circulation. By slurrying the waste in water or in the pickling acid solution and filtering out the water, a homogeneous cake is obtained and it is easy to add and evenly mix different kinds of additives in the slurry as needed. Due to the slurry, it is advantageous to use different types of waste water that comes from the factory. The invention will be described in more detail below with reference to the accompanying drawing, which shows a process diagram intended for applying the method according to the invention.

The process according to the invention comprises the following unit processes: Incorporation of dry dust 1 in the neutralization slurry 2, pressure or vacuum filtration 3, drying preheating 4, in which melting gases and reducing melting 5 are used. The process scheme 'has been shown in the figure.

All stored dry waste 1 is mixed into the neutralization slurry in a mixer 2, so that the pH is above 7 and advantageously about 9-10 and filtered in a pressure or vacuum filter 3. The solution 9 is returned to the slurry 2. In connection with the slurry, lime and Fe sulphate, by means of which the filtration and strength properties of the filtered cake are regulated together with the precipitation from the neutralization plant. At the same time, Cr is reduced to Cr3 +. Some or all of the reducing agent (coke or coal) can also be added at this stage.

From the filtration 3 a cake is obtained whose moisture content is 15-40% and compressive strength in the moist state of the order of 20-30 kg / M cm 2, which is sufficient to withstand the mechanical stresses during drying. During drying, the compressive strength increases. When the cake falls down from the filter, the pieces suitable for melting are crushed.

The pieces of the filter cake are fed 10 in a belt or drum dryer 4, where the drying and preheating is effected = on combustion of reducing gases 11 from the melting furnace. Any external energy, ie. other than the combustion heat of the reducing gases is not needed. The flue gases 12 are purified before discharge to the chimney.

The preheated material 13 as well as the added coke and any additives required are fed into an electric furnace 5, in which the reduction, melting and formation of CO gas takes place. A metal mixture 6 is obtained which contains precious metals and slag 7, which are removed periodically, as well as dusty flue gases 14. The yield of iron, chromium, nickel and molybdenum in the metal mixture 6 is 85-95%. From zinc and lead, 94-98% passes into the dust. ,. øña. The dust-containing flue gases l4 are purified and the CO-containing gas l1 is blown in for the combustion in the drying drum 4. The separated dust 8 which has a high zinc and lead content continues for further treatment.

By means of the treatment processes for the waste described above, it is possible to combine the treatment of all waste metal-containing, valuable metals related to the function of a stainless steel plant, and in addition achieve a remarkably high yield of the metals. In addition, on the basis of test runs on a pilot scale, it has been established that the treatment does not entail harm to the environment, since in connection with the treatment the hexavalent chromium is reduced to trivalent and the oils are bound to the waste. An advantage of the treatment is that the process obtains a non-polluting waste which is suitable for the landfill or an easily storable and all waste containing intermediate product, a filter precipitate from which, in connection with new melting, a Fe suitable as a raw material is obtained. -Cr-Ni-Mo metal mixture, an abundant zinc and lead containing dust suitable for utilization and dumpable waste slag.

The process is cheap both in terms of its operating costs and investment costs. Through the process, occupational hygiene and environmental problems can be avoided, as the dam is slurried and the hexavalent chromium is reduced to trivalent. The waste can already be pre-treated at each steel plant or combined in a central treatment plant.

The invention has been described above in connection with the treatment of dust from the steel industry. The invention is also equally suitable for the treatment of metallurgical dust of other kinds. 1470 kg of waste mixture containing pickling acid slurry, blasting dust, gas purification dust and abrasive wool from an AOD converter, 50 kg of lime, 20 kg of ferrous sulphate and 80 kg of coke was slurried 2 in water, the pH being about 10, and filtered, l640 kg of cake was kept, the humidity of which was 30% and which was dried and preheated in a drum 4. The temperature of the dried product was 35 ° C. CO gas was consumed 180 m3 and combustion air 430 m3.

Dough dough and 80 kg of coke were melted in an arc furnace 5. Man Qnhö fi l metal mixture 340 kg, slag 340 kg and dust 170 kg, whose analyzes were as follows: ë: '. Fi = f ~ §': ï :: “. '* “:' - 'É 7902955-9 Metal mixture slag Damm Fe 72.3 3.5 0.9 Cr' 13.5 2.3 0.4 Ni 10.1 0.5 0.1 Zn 0.03, 0.03 6.2 Pb 0.06 0.06 3.5 Mo 1.2 0.06 ». Sioz 10.0 Å 6.0 CaF2 41.0 35.8 'Cao _ 32.2 21.2 The temperature of the metal mixture was 150 DEG C., the slag 160 DEG C. and the removal gases of the removed gases. Electricity was consumed 900 kWh. The metals were divided into the metal mixture, the slag and the dust as follows: Fe Cr Ni Zn Pb Mo Metal mixture% 95.0 85.0 94.2 0.9 3.1 95.5 Sl fl øø% 4.5 13.7 4.9 0, 9 3.1 45.5 Dust% 0.5 1.3 0.8 98.2 93.8 ~ It is clear that the filtered cake can be dumped if its further treatment is not profitable. The waste does not pollute the environment and can thus be transported to the landfill without risk. If desired, such waste can be further treated in any known manner for the recovery of the precious metals therein.

Claims (4)

7902955-9 P a t e n t k r a v Process for the treatment of metallic dust and waste from the metallurgical industry, characterized in that the waste to be treated is suspended in water or in a pickling acid slurry, the slurry is added to ferrous sulphate and to reduce hexavalent chromium present in the waste to trivalent, the pH of the slurry is adjusted a value above 7 in order to precipitate heavy metals in the slurry, lime is added in order to regulate the filtration properties of the slurry and the strength properties of the filtered cake and the slurry is filtered into a cake which is transferred in pieces. 2. » Method according to claim 1, characterized in that the slurry is filtered into a cake whose moisture content is about 15-40% by weight and compressive strength about 20-30 kg / cm 2. 3. A method according to claim 1 or 2, characterized in that the drying and preheating of the filtered moist waste is carried out by means of hot gases produced by combustion of carbon monoxide-containing flue gases coming from the reducing melt. 4. A method according to claim 1, 2 or 3, characterized in that the piece-shaped filter cake and carbonaceous reducing agent are melted in an electric oven. šç