Use of New Processing Materials during Slag Depletion in Nadezhda Metallurgical Plant Slag-Cleaning Furnaces

Within the period of 2015–2017 at Nadezhda Metallurgical Plant (NMZ) the following new processing materials are tested to reduce pyrometallurgical slags: quartzite from the Shilkinsk deposit of Krasnoyarsk Territory (as a flux instead of overburden rock produced locally) and anthracites of various grades (as a reducing agent). The materials tested are attractive in terms of their price compared with the flux and reducing agent (coke) used currently. During the tests with imported quartzite in the process of electric-furnace slag reduction the specific flux consumption falls by 36.9% and the specific electric power consumption falls by 3.2%. There is no marked wear of protective accretions in the slag zone of the furnaces and there is no unfavorable effect on the level of hearth scale. Standard waste slag is produced. Various anthracite brands are tested industrially (i.e., AM-UHG, AKO-UHG produced by Listvyanskaya Mill of CJSC Siberian Anthracite, AKO brand manufactured by LLC Promprodukt, A of AO grade produced by LLC Southern Fuel Company). Tests show that an increase in anthracite fraction in the total amount of the reducing agent supplied for smelting causes undesirably low matte metallization with poor non-ferrous metal extraction into matte, especially cobalt. This results in increased specific consumption of the reducing agent per ton of charge processed in a slag-depletion electric furnace (SEF). Based on tests, the following order for matte metallization degree (in descending order) is obtained: AKO > A of AO grade > (mixture of AM-UHG and AKO-UHG). Testing of the first brand is stopped prematurely due to the abrupt critical reduction of matte metallization (up to 17.8% with a specified minimum value 19%) and low level of hearth accretion in the SEF, likely to fall below the point required for bottom protection. Taking account of the results obtained quartzite from Shilkinsk deposit is recommended for industrial use in order to reduce converter and FSF slags in the electric furnace. Anthracites of AM-UHG, AKO-UHG and A grade of AO are recommended for the partial replacement of the reducing agent used (from 50 to 75%), apart from the sample of AKO grade.