848
T. Yue et al.
Introduction
For the green production and sustainable development of environment, the treatment
of industrial hazardous solid waste has received more and more attention. In nonferrous metals hydrometallurgy industry, millions of tons of hazardous iron oxide
residues are produced during the iron removal process in sulphate leaching solutions.
Iron is present as an undesirable constituent in zinc, copper, and nickel concentrates,
and the solubilisation of the desired metals during the leaching process also leads to
dissolution of iron into the solution. Iron constitutes an impurity in leaching solutions,
which must be removed before electrolysis.
In most existing hydrometallurgy plants, iron is removed by its precipitation as
jarosite and goethite. Impounding large amounts of residues from the jarosite process in tailings ponds incurs high operating cost. The exposure of these residues to
atmospheric conditions will cause severe environmental problems, due to the presence of heavy metals and/or hazardous elements, such as Zn, Ge, In, Pb, Se, and S.
Furthermore, it is difficult to use jarosite residue because the Fe content in jarosite
is lower than 30% with high fluctuation in the content of other undesired elements.
Compared with jarosite residue, goethite residue has a lower volume and a higher
Fe content (more than 40%), and contain a small amount of impurity elements. At
the same time, it is possible to use this residue as an iron source in iron making after
suitable treatments. Most electrolytic zinc plants use calcium hydroxide or calcium
carbonate as neutralizer in the goethite process, which introduces no impurity into
the solution and has a relatively low cost. However, using calcium carbonate or calcium hydroxide led to co-precipitation of calcium sulfate with goethite precipitates,
resulting in the difficulty in utilizing these residues. As a result, the residues have
to be impounded in tailings ponds which pose great threat to local soil, water, and
atmosphere by contained heavy metals and/or hazardous elements in the residue,
such as Zn, Ge, As, and S.
To treat these progressively expanding hazardous residues, a novel method is
developed in this study to convert these hazardous residues into secondary resources.
To accomplish this objective, maghemite fine particles are introduced first into the
goethite process as the nucleus seeds to promote goethite precipitation, imposing
the required magnetism of goethite precipitates from the attached maghemite fine
particles. The magnetically responsive goethite precipitate-maghemite composite
particles are separated from calcium sulfate precipitates using a magnetic drum separator. After appropriate treatment to remove the hazardous impurities, the produced
goethite-maghemite composite particles and the separated calcium sulfate can be
used as ironmaking raw material and building material, respectively. This paper
reports the results of addressing a long-term impoundment problem of the hazardous
iron residues in smelters with our novel method.
T. Yue et al.
Introduction
For the green production and sustainable development of environment, the treatment
of industrial hazardous solid waste has received more and more attention. In nonferrous metals hydrometallurgy industry, millions of tons of hazardous iron oxide
residues are produced during the iron removal process in sulphate leaching solutions.
Iron is present as an undesirable constituent in zinc, copper, and nickel concentrates,
and the solubilisation of the desired metals during the leaching process also leads to
dissolution of iron into the solution. Iron constitutes an impurity in leaching solutions,
which must be removed before electrolysis.
In most existing hydrometallurgy plants, iron is removed by its precipitation as
jarosite and goethite. Impounding large amounts of residues from the jarosite process in tailings ponds incurs high operating cost. The exposure of these residues to
atmospheric conditions will cause severe environmental problems, due to the presence of heavy metals and/or hazardous elements, such as Zn, Ge, In, Pb, Se, and S.
Furthermore, it is difficult to use jarosite residue because the Fe content in jarosite
is lower than 30% with high fluctuation in the content of other undesired elements.
Compared with jarosite residue, goethite residue has a lower volume and a higher
Fe content (more than 40%), and contain a small amount of impurity elements. At
the same time, it is possible to use this residue as an iron source in iron making after
suitable treatments. Most electrolytic zinc plants use calcium hydroxide or calcium
carbonate as neutralizer in the goethite process, which introduces no impurity into
the solution and has a relatively low cost. However, using calcium carbonate or calcium hydroxide led to co-precipitation of calcium sulfate with goethite precipitates,
resulting in the difficulty in utilizing these residues. As a result, the residues have
to be impounded in tailings ponds which pose great threat to local soil, water, and
atmosphere by contained heavy metals and/or hazardous elements in the residue,
such as Zn, Ge, As, and S.
To treat these progressively expanding hazardous residues, a novel method is
developed in this study to convert these hazardous residues into secondary resources.
To accomplish this objective, maghemite fine particles are introduced first into the
goethite process as the nucleus seeds to promote goethite precipitation, imposing
the required magnetism of goethite precipitates from the attached maghemite fine
particles. The magnetically responsive goethite precipitate-maghemite composite
particles are separated from calcium sulfate precipitates using a magnetic drum separator. After appropriate treatment to remove the hazardous impurities, the produced
goethite-maghemite composite particles and the separated calcium sulfate can be
used as ironmaking raw material and building material, respectively. This paper
reports the results of addressing a long-term impoundment problem of the hazardous
iron residues in smelters with our novel method.