Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1999-04-13
2001-02-27
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S419100, C423S165000, C423S163000, C423S162000, C423S158000, C423S155000, C162S189000
Reexamination Certificate
active
06193945
ABSTRACT:
The present invention refers to a method of recovering calcium from waste material or contaminated natural calcic material. The present invention also refers to the use of calcium recovered by such method.
High grade calcium carbonate is used in a variety of products, e.g. as filler or pigment in paper, paint, polymers, tooth paste etc. Virgin or natural calcic material is used for the production of fillers and pigments. A plurality of new calcium mines or quarries have to be opened in order to fulfil the need, these new quarries causing undesired changes in the landscape and environment. In spite of new opened quarries calcium carbonate often has to be transported over long distances, which increases the costs of filler and pigment.
At the same time growing depots are need to store residues, rejects, refuse and different kinds of waste material, which contains calcium. These depots, besides probably causing pollution, also cause undesired changes in the landscape and environment.
The object of the present invention thereby is to provide a recycling method, according to which CaCO
3
may be recovered from all types of residues, such as from rejects and refuse from various production processes and even from municipal waste, which contain calcium.
A further object of the present invention is to provide a method for recovering of calcium from such heavily contaminated natural calcic materials in old mines and quarries, from which it has not until now been economically feasible to recover calcium for use as pigment in paper production.
It is also an object of the present invention to provide a method for recovering calcium from residues, rejects, refuses and waste material, in order to substantially reduce the volumes of waste and the costs for handling of them. This is a very important object of the present invention when considering the continuously decreasing space for waste disposal and the need to decrease pollution.
It is a still further object of the present invention to provide a method for recycling high-grade calcium carbonate in order to thereby substantially decrease the need to open up new mines or quarries for extracting natural calcium carbonate.
The present invention for recovering calcium from waste material or contaminated natural calcic material is characterized by what is stated in the appending claims. Thereby calcium may according to a preferred embodiment of the present invention be recovered from waste or contaminated natural calcic material by a method including following consecutive steps:
(a) providing waste material or contaminated natural calcic material in which the calcium compounds are mainly in an acid soluble form, such as CaO and CaCO
3
;
(b) preparing an aqueous suspension of said material in step (a);
(c) lowering the pH of said aqueous suspension in step (b) to pH<6, preferably pH<4, by mixing an acid such as HCl or HNO
3
therein, for providing a suspension including an acidic liquid phase containing said calcium compounds and other compounds, such as aluminium, silicate and/or magnesium compounds, present in acid soluble form;
(d) raising the pH of said acidic liquid phase in step (c) to pH>6, preferably pH>7, by mixing a base, such as NaOH therein, for precipitating the main portion of aluminium compounds present in said liquid phase and thereby providing
a solid phase, including the precipitated aluminium compounds and other non-soluble impurities, and
a neutral or basic liquid phase, including the main portion of said calcium compounds in soluble form;
(e) separating said solid phase from said neutral or basic liquid phase in step (d);
(f) carbonizing said neutral or basic liquid phase in step (e), e.g. by introducing Na
2
CO
3
or NaHCO
3
therein, for precipitating said calcium compounds as CaCO
3
, and
(g) separating the precipitated CaCO
3
in step (f) from said neutral or basic liquid phase.
In step (c) pH of the aqueous phase should in most cases preferably be lowered to pH<4 or even less, such as pH<3, for a maximal dissolution of compounds.
Should the waste material, from which calcium compounds are to be recovered, be in a non-soluble form, then a pre-treatment step is needed, in which the waste material is burned to provide an ash which contains calcium compounds in an acid soluble form, such as CaO or CaCO
3
. The waste material may e.g. be a composite material including calcium compounds mixed with polymer, the polymer preventing calcium compounds from being mixed with acid and dissolved. By burning the polymer material a residue including readily soluble calcium oxide or calcium carbonate is achieved. All kinds of industrial reject material or recycled waste material, such as waste paper, or municipal refuse in liquid or solid form, may first be burnt to provide calcium oxide or calcium carbonate in an easily soluble form.
It is in most cases recommended that non-soluble compounds are separated from the suspension after step (c) before raising the pH level to pH>6. Most waste materials include non-soluble compounds which are not soluble in acidic liquid. These compounds should preferably be separated from the acidic liquid and be further treated in separate recovery processes or be deponed for possible later use not disclosed here.
In step (d) different acid soluble compounds may be precipitated in one single step or in a plurality of separate precipitation steps, depending on which compounds are to be recovered separately and which may be separated as mixed material. E.g. in precipitating step (d) pH of the liquid phase may be raised in one single step (by the addition of e.g. NaOH) to a suitable pH level at which e.g. aluminium, silicates and magnesium compounds are precipitated together. In many applications, however, it may be desirable to perform the precipitation in two or even more separate steps, thereby e.g. raising pH in a first pH raising step to a pH level between pH 5-pH 9. and in a second pH raising step to a pH level between pH 10-pH 12. Precipitated solid compounds are separated from the suspension after each pH raising step. Typically aluminium compounds precipitate at a pH range between pH 5-pH 9. In the second precipitating step in a pH range between pH 10-pH 12 solid compounds, such as magnesium compounds may be separated from the liquid phase.
In order to separate calcium, which e.g. is present as CaCl
2
and/or Ca(OH)
2
, the neutral or basic liquid phase, from which precipitated solid particles have been separated, may in step (f) be carbonized by introducing Na
2
CO
3
or NaHCO
3
therein. The calcium carbonate precipitates and may be separated as a very clean product.
In order to enhance the precipitation of impurities and other solid material from liquid phase in step (c) or step (d) a coagulant, such as an aluminium based coagulant, may be introduced into the liquid phase. Aluminium, present in the waste material and/or added as coagulant, precipitates typically in gel like form, which tends to improve the separation of other solid material, such as heavy metals, from the liquid phase. A flocculant may be introduced into the basic liquid phase for enhancing separation of solid compounds there from.
Different ways of separating precipitated solid material from the liquid suspension are available, such as sedimentation, filtration, flotation or centrifugal separation.
The present invention provides a very efficient method for recovering calcium compounds from a most different residues or waste materials, for re-use, e.g. as filler, coating material or pigment in a variety of products, such as in paper.
Also natural heavily contaminated calcic material can be easily cleaned for normal use.
The present invention thereby provides a method which decreases the need to open up new calcium mines or quarries, which tend to destroy landscape and environment. Calcium can be recovered close to the cite where it is to be used, which decreases need for transportation. Also the present invention has an impact on waste material deponed, which do not have to grow as fast as today if the amount a
Betz Günter
Blomquist Markus
Griffin Steven P.
Nave Eileen E.
Nixon & Vanderhye P.C.
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