The aim of this research project is to develop a process that allows reclamation of zinc from secondary materials containing zinc, zinc oxide or zinc sulphate, leaving ecologically acceptable residues.
This study has identified a need for the recycling of waste from zinc consumer industries, both from an economic point of view and with respect to the environment. Analysis of secondary material revealed high levels of zinc in foundry ashes, zinc oxides from brass and bronze production, electric arc furnace (EAF) dust and slags. Due to the toxicity of some wastes the use of landfills is particularly unattractive.
The treatment processes available (pyrometallurgy, hydrometallurgy or pyrohydrometallurgy) for reclaiming zinc were studied with respect to their suitability of different types of waste. This identified the feasibility of the MODIFIED ZINCEX process, initially not considered, with advantages on other processes for sonie types of residue.
The MODIFIED ZINCEX process was tested initially on a laboratory scale using samples of galvanizing ashes; steel fumes; copper and zinc residues from brass, copper and bronze smelting industries; and Waelz oxides. The first step of the process is acid leaching. Treatment with sulphuric acid gave 90% (or greater) solubilization of zinc in all wastes except steel fumes (76%). A precipitation step is used to eliminate impurities coleaching with the zinc such as iron and aluminium. Solvent extraction forms the most important stage of the MODIFIED ZINCEX process, its function being to purify and concentrate the zinc solution obtained following the zinc electrowinning. Organic solvents, aqueous solvents, temperature, and stripping and extraction isotherms were studied in order to optimize the extraction step. The best route for disposal of effluent from the MODIFIED ZINCEX process determined for each type of raw material.
A process simulation computer model was developed to further assess the feasibility of this process.
Complementary tests were performed for each stage of the process in order to assess the behaviour of solid-liquid separation (decantation and filtration).
The process was demonstrated in continuous, pilot plant, steady state operation. Zinc recovery was determined for each type of waste: Waelz oxides, 95%; galvanizing residue, 97%; Irish steel fumes, 86%; and Iberian steel fumes, 67%. SHG zinc quality (99.99%) was produced.
The cost of setting up and running a full scale processing plant was determined, showing that for all types of waste to process was economically viable.
In this work there are 4 main activities. Firstly, knowledge of the actual situation of zinc residues. The initial path will study existing zinc processing units, determining the volume and composition of residues being originated. The work is divided into 2 subactivities: defining the status of the industries producing zinc, their oxides and salts and defining its residue production rates, and stocks, taking into consideration its composition, disposal, local regulations and foreseeable future.
Secondly, knowledge of the actual disposal cost. The subactivities are: study of the existing treatment processes to which those residues are subject today and determination of the disposal costs today as well as a revision of its future evolution.
Thirdly, testing of the TR process. The tests have the following aims:
to establish the technical applicability of these residues, via laboratory studies, determining the zinc recoverability from them;
to produce a computer model of the process that will allow determination of the costs of its application at any capacity scale;
to polish the optimization of the operating conditions, from the early results with every sample;
and to demonstrate in continuous, bench scale, steady state operation, the performance of the process with the most convenient sample.
Finally, a feasibility study of the proposed technology. This will:
define design parameters and operating conditions of the industrial plant;
estimate the capital cost of the plant, through the production of a computer programme incorporating a data bank of technical and economical data;
define the ecological impact, or ecological cost saving in processing the residues through the TR process;
and consider the economical feasibility in different scenarios.
Funding SchemeCSC - Cost-sharing contracts