Process for reducing the amounts of zinc (ZN) and lead (PB) in materials containing iron (FE)

Abstract

The present invention relates to a process for reducing the amounts of zinc and lead in starting materials comprising iron which comprises the steps of: —selectively leaching Zn and Pb comprised in the starting materials by mixing the starting materials with hydrochloric acid and an oxidizing agent comprising at least 5 wt-% of manganese dioxide in one or several reactor(s) at a temperature superior or equal to 35° C. and at a p H comprised between 0.5 and 3.5, —filtrating the mixture obtained in order to separate the solid and the filtrate, —washing the solid with water, the resulting solid comprising mainly Fe, a reduced amount of Zn and Pb compared to the original starting materials, —recovering the filtrate of step b) and the washing water of step c) which comprise chloride, solubilized Zn and Pb in one or several reactor(s), —precipitating solubilized Zn, Pb in the recovered filtrate and the washing water by mixing with a neutralizing agent, —filtrating and washing the solid residues obtained in step e) in order to remove the chloride from the solid residues which comprise at least Pb and Zn. The present invention also refers to the use of the materials obtained after treatment in a in a sinter plant and blast furnace or in all pyrometallurgical furnace which value iron such as electrical arc furnace (EAF), cupola furnace, oxycup furnace, submerged arc furnace (SAF), a plasma furnace, rotary hearth furnace.

Description

TECHNICAL FIELD[0001]The present invention generally relates to the treatment of starting materials comprising iron (Fe), zinc (Zn), lead (Pb) and possibly carbon (C) by hydrometallurgy process and in particular to the removal of Zn and Pb from these starting materials.BACKGROUND ART[0002]The chemical and metallurgical industries generate various forms of wastes containing pollutant elements. For example, the steel making industry involves the use of blast furnace for smelting in order to produce industrial metals such as pig iron and the use of basic oxygen furnace (BOF) in order to produce steel from pig iron. Blast furnace and BOF in operation produces a lot of dusts and sludge at the outlet of the gas cleaning plant. These sludge or dusts are composed of different metals. In particular, these sludge or dusts comprise iron, carbon, zinc and lead. In order to reduce the operating cost linked to the operations of such industries, it is desirable to recycle these materials in order ...

AI Technical Summary

Benefits of technology

The patent text describes a simple and efficient process that helps remove zinc and lead from materials made of iron and possibly carbon. This process doesn't require expensive chemicals and can be easily carried out.

Problems solved by technology

Although these sludges (or dusts) comprise iron and carbon, which could be recycled to recover contained metals, the presence of zinc and lead prevents the reuse of these sludge or dusts.

It is thus impossible to recycle directly these materials without affecting the blast furnace operation.

Thus, the sludges (or dusts) comprising zinc and lead cannot be recycled to the sinter plant in order to be retreated by the blast furnace.

However, this constitutes a major environmental and economic problem.

Indeed, the storage of this kind of materials can be detrimental for the environment since the contaminants can affect the surrounding soils or ground waters.

This may be a real threat for the health and more specifically for the fauna and flora.

Furthermore, even from an economic point of view, the dumping of these materials cannot be regarded as an advantageous solution.

Indeed, the available place for internal dumping in plant area decreases whereas the costs linked to the external dumping increase.

However, this type of process shows several drawbacks.

One of the main drawbacks is that it relies on the availability of a picking line acid in the steel plant.

Indeed, not all of the steel plants have picking line acid.

Thus, this type of process is limited to only specific steel plants.

Another drawback is the oxidation of Fe II to Fe III in the pickling line for the goethite precipitation.

But, the kinetics of oxidation of iron, in acidic condition and in high chloride media, are very slow.

Such a reaction would thus require costly equipment to handle such oxidizing agents.

As a result, the processes involving pickling line acid cannot be applied to every kind of plants and furthermore are not economically interesting.

Working under high pressure and temperature as described in this document is however economically and operatively not preferred for industrial applications as it requires pressure vessels made out of costly high grade material and involves higher safety requirements.

More generally, there is no satisfying and profitable process resulting in the selective removal of zinc and lead from a starting material matrix comprising iron.

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