Electrometallurgical Method for Ferromanganese Ore Processing
The preparatory processes for ore treatment require further metallurgical extractions, FMNs dehumidification at the temperature of 350-400оС during 30-40 min so that to bring the residual humidity to 5%, maximum. If the FMNs humidity is lower, they are more efficient for overgrinding.
The apparent density of (dry) FMNs also had regional variations from 1.6 to 1.94 gr/cm, the porosity was from 30 to 49.5%, the bulk density of dry (base) nodules did not exceed 1.04-1.18 gr/cm3. The porosity of nodules reached 60%, the apparent specific weight – 1.5 gr/cm3, the true weight – 3.8 gr/cm3.
For the further extraction of dehumidified FMNs it is necessary to conduct prior selective conversion to the metallic phase of copper, nickel, cobalt (up to 90%), while the iron reduction degree is limited (60-70%), and the manganese is almost entirely remains in its oxidic form.
The optimal parameters that control the reduction of FMNs with hydrogen at the selective enrichment stage are: temperature - 800-850оС, duration - 20-30 min. The reduced copper, nickel, cobalt, iron remain in the treated product in the form of the metallic phase of a microscopic size.
For recovery purposes, the specialists elaborated an electric smelting technology (1,450-1,500оС) with the aim to obtain a complex alloy (Си + Ni t Со) > 20% and charge slag with 34-35% Mn and < 0.015% P.
The peculiarity of the designed process is electric smelting of a selected, enriched in a hydrogen atmosphere, FMN-product, without adding any carbonaceous or other reducers. This allows obtaining an alloy rich in nickel, cobalt, copper with limited conversion of iron and retention of almost all manganese in slag.
The slag enriched in manganese and obtained as a result of smelting of selectively enriched FMNs can be used for smelting high-carbon ferromanganese (76-84% Mn; 0.12-6.0 81; 4.7-6.956% C; 0.04-0.5% P). In case of a different base-to-acid ratio (СаО)/ (810) = 0.79-1.41, the manganese recovery was equal to 73.5-78.8%, while the slag ratio was 1.13-1.55.
There are a lot of foreign patents where the basic stage of FMNs metallurgical processing is firing of FMNs in rotary or shaft furnaces for the purpose of selective conversion into a metal form of copper, nickel and cobalt.
At the next stage, the ash should be melted in a reverberatory or electric furnace in order to obtain a complex alloy Ре-Си-Ш-Со system and high-manganese low-phosphorus slag. At the third stage, this slag is used to obtain manganese products. The nodules (0.5-2.2% Ni; 0.1-1.5% Со; 0.3-2.0%1 Cu; 4-17% Fe; 12-34% Mn) are heated in reducing conditions at the temperature of 750оС, but lower than 1,110оС to obtain liquid metal and first manganese slag.
Then, the liquid alloy is aerated (with oxygen) to obtain a liquid alloy and the second manganese slag. At the third stage, the liquid alloy is sulphidized to obtain matte. The nickel recovery may reach 97.8%, copper – 94.5%, cobalt – 96.5% and iron 18.5%. The slag is used as a raw material containing manganese.
The nature of the three-stage pyrometallurgical reduction of oceanic FMNs consists in the following:
At the first stage, FMNs are prepared for a reduction smelting process. We suggest two variants for FMNs preparation.
At the second stage, the nodules prepared according to methods A and B are melted in furnaces, while the reducing agent is added to the shaft assuming more complete reduction of nickel and cobalt, a bigger portion of copper and 1/3 of iron, taking into account the return of a “remelted alloy” containing such reducing agents as manganese and silicon. The product of the smelting process is a primary alloy containing almost the entire amount of nickel, cobalt, =3/4 of copper, =»1/3 of iron and a small amount of manganese, and sometimes molybdenum, as well as slag containing almost all manganese, 2/а of iron and 74 of copper, small amount of nickel, cobalt, sometimes aluminium and titanium, and 8Ю2, СаО, А1?0.,, existing in FMNs.
The slag and the alloy are tapped from the furnace through two tap-holes placed at different levels. At the third stage, the additional extraction of *[/4 of copper remaining in the primary slag together with a small amount of nickel and cobalt takes place.
For this purpose, the liquid primary slag is treated in one or two train casting ladles with ferrosilicon (75% Si). The product resulting from treatment in ladles is the so called secondary alloy (containing Сu, Ni, Со, Mn, Fe, Si), that is returned to the second stage as a reducing agent, and the secondary slag containing manganese, iron, oxide admixtures, and nickel and copper oxides. It is recommended to use the slag for the smelting of silicomanganese and (or) ferromanganese.