METHOD OF RECOVERING VALUABLE METALS FROM WASTE

Abstract

A method which allows recovery of valuable metals in simple steps from printed wiring board or the like is provided.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of recovering valuable metals from wastes such as IC circuits board and printed wiring board.

2. Description of the Related Art

Printed wiring boards commonly used in personal computers and cell phones contain significant amounts of metals used therein.

Specifically, printed wiring boards have an insulation board such as glass epoxy substrate and semiconductor elements, capacitors, resistors, and wirings in combination formed thereon, and generally, the organic component content is said to be 32%; the glass component content, 38%; and the metal component content, about 30%.

Most of the organic matter is an epoxy resin, and approximately 66% of the glass components is SiO₂.

In particular, the metal materials are said to contain copper in the greatest amount and additionally valuable metals such as tin, iron, lead, nickel and gold in an amount of 0.1% in the printed wiring board.

Because these wastes contain a great amount of precious valuable metals, various methods of recovering the metals were developed and commercialized.

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-301225.

Patent Document 2: Japanese Patent Application Laid-Open No. 2001-259603.

SUMMARY OF THE INVENTION

The conventional recovery methods described above, i.e., methods of recovering metals by dissolving the printed wiring board in acid or heating it and then oxidizing or pulverizing it, have the following problems:

<1> The glass fiber therein melts in the heating step into a melt-solidified solid state containing the metals inside.

<2> Incineration at high temperature leads to increase of the loads both on the apparatus and the environment.

<3> Fusion or electrolysis at high temperature demands great amounts of fuel and power.

<4> Although it is possible to dissolve the glass fiber in acid more efficiently by pulverization thereof, the fibrous material is tough and thus difficult to pulverize.

An object of the present invention, which was made to solve the problems above, is to provide a method of recovering valuable metals from waste, the waste being an integrated industrial waste containing a glass fiber, an epoxy resin and valuable metals such as copper, iron, gold and aluminum, comprising heating the industrial waste to a temperature at which the glass fiber does not melt but degrades, removing the degraded glass fiber, and thus, recovering the valuable metals contained in the waste.

As described above, the method of recovering metals from waste according to the present invention has the following advantages:

<1 > The method allows recovery of valuable metals in simple steps without need for an additional step of pulverizing the melt-solidified glass fiber.

<2> The method does not demand heating or fusion at high temperature and is thus, lower in concern about environmental pollution, and can be used in countries where stricter laws and regulations are imposed.

<3> The method demands smaller amounts of fuel and power and is thus economical.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1(A) is a photograph showing printed wiring boards heated respectively under temperature-period conditions in the range of 300° C. for 10 minutes and 750° C. for 20 minutes.

FIG. 1(B) is an English translation in table form of the Japanese characters shown in FIG. 1(A).

FIG. 2(A) is a photograph showing printed wiring boards heated respectively under temperature-period conditions in the range of 750° C. for 30 minutes and 1000° C. for 40 minutes.

FIG. 2(B) is an English translation in table form of the Japanese characters shown in FIG. 2(A).

FIGS. 3 to 34 are photographs of a heated printed wiring board.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Hereinafter, favorable embodiments of the present invention will be described in detail with reference to drawings.

EXAMPLES

<1 > Wastes to be Processed

The industrial wastes processed by the recovery method according to the present invention are industrial wastes such as printed wiring boards.

These industrial wastes are characteristic in that they are integrated materials of a glass fiber, an epoxy resin and valuable metals such as copper, iron and gold.

<2> Heating Step

These industrial wastes are heated at a particular temperature for a particular period of time.

The temperature and the period are such that the glass fiber does not melt but decomposes.

The relationship between the temperature and the period was determined in many tests.

The results showed specifically that the industrial waste is heated favorably under a condition in the range of 500° C. for 20 minutes or more and 1000° C. for 10 minutes or less.

More favorable results are found to be obtained, when the industrial waste is processed under a condition in the range of approximately 750° C. for 30 minutes or more to 1000° C. for 10 minutes or less.

Here, the “favorable results” mean that the glass fiber and the valuable metals are separated and only the valuable metals are recovered easily.

<3> Reason for Selecting the Temperature and the Period

<3-1 > Determination of Upper Limit

The temperature and the period above are selected, because the glass fiber melts when heated under a temperature/period condition severer than the temperature/period condition above and solidifies itself when cooled.

The melted glass fiber solidifies itself into a solid state, while enclosing the metals therein, prohibiting recovery of the metals from the state once formed.

For that reason, the metals have been recovered after the metals and the glass fiber are both melted at high temperature, by using the difference in specific density.

However, by the method according to the present invention, wherein the waste is heated up to 1000° C. for 10 minutes or less, the glass fiber does not melt, eliminating the possibility of the glass fiber melt-enclosing the metals.

<3-2> Determination of Lower Limit

As for the lower limit heating condition, the glass fiber sheet, when heated at 500° C. for 20 minutes or less, retains its original shape and still contains the metals therein without separation, although the surface thereof turns brown in color.

The glass fiber sheet in that state is resistant to pulverization under pressure and cannot be separated from the metals.

<3-3> Determination of Optimal Temperature and Period

However, the glass fiber sheet and the metals are separated actually, when heated under a condition in the range of 500° C. for 20 minute or more to 750° C. for 30 minutes or less.

It is thus possible to make the metal components sediment and collect the metal sediment, while separating it from the glass fiber sheet, for example, by gravimetric sorting by using a liquid.

The lower limit heating condition is more preferably approximately 750° C. for 30 minutes or more.

In the temperature-period condition above, the glass fiber sheet apparently retains its plate shape as a sheet, but is pulverized easily under external force, for example by the force when the sheet is held with fingers.

In addition, the metals do not melt in the temperature range.

Therefore, the glass fiber is pulverized easily by slight vibration or pressurization by roller, favorably allowing recovery of the metal components as they are.

<4> Test Results

Printed wiring boards were heated in various temperature conditions of upward from 300° C. for 10 minutes at intervals of 100° C. and 10 minutes.

The results obtained in respective temperature-period conditions are shown in photographs of FIGS. 3 to 46, and the results are summarized in the following Table 1.

TABLE 1

The marks in respective columns are as follows:

x The fiber sheet and the metals retain their shapes and are not
  separated from each other.
  In particular at the low temperature side, the fiber sheet is only
  discolored.
  The fiber sheet retains its original shape, even when pressurized by
  hand.
Δ The fiber sheet and the metals are separated from each other.
  Thus, the valuable metals can be collected.
  However, the fiber sheet retains its shape and is resistant to
  pulverization.
∘ Apparently, the fiber sheet retains its shape.
  However, it is pulverized easily by slight pressurization or by
  the force when it is held with fingers.
  Because the glass fiber can be pulverized easily into powdery, it is
  possible to separate the valuable metals easily from the powder.
□ The glass is solidified into an aggregate state, while holding the
  metals.
  Aggregates as hard as rock are obtained when the waste is heated at
  higher temperature for an elongated period.
  The metals, which are entrapped in the melted glass, are difficult to
  separate.

There was no change in the samples if they were heated for an extended period of time, even though the results obtained are not described herein.

<5> Heating in Oxygen-free State

It is possible to heat wastes in oxygen-free state, for example by using an electric furnace.

In this way, it is possible to recover valuable metals as they are without formation of oxide films, because the surface of the valuable metals such as copper are not oxidized.

If there is a concern about the damage of the heating unit in electric furnace, the waste may be heated in a low-oxygen state generated by burning carbon additionally as the heat source.

<6> Step of Removing Glass Fiber

When heated in a temperature-period condition in the range above, in particular when heated in the range of 500° C. for 20 minutes or more and 750° C. for 30 minutes or less, the glass fiber sheet mostly retains its original shape but is separated from the valuable metals.

It is thus possible to recover the valuable metals, by separating the glass fiber sheet from the valuable metals in the later separation step by using an optimal method such as gravimetric separation.

Further, when heated in the range of 750° C. for 30 minutes or more, the glass fiber degrades to such a degree that it is pulverized easily into powder by application of slight external force, such as that when the glass fiber is held with fingers, or by application of vibration or pressure.

On the other hand, the glass fiber does not melt, because the heating temperature-period condition is 1000° C. for 10 minutes or less, and thus, the metal components remains as they are without entrapment in the melted glass fiber.

It is thus possible to separate valuable metals from the glass fiber, removing the glass fiber and recovering the valuable metals, by a known simple method such as sieve classification or gravimetric classification.

Claims

1. A method of recovering valuable metals from waste, the waste being an integrated industrial waste containing a glass fiber, an epoxy resin and valuable metals such as copper, iron, gold and aluminum, comprising heating the industrial waste to a temperature at which the glass fiber does not melt but degrades,removing the degraded glass fiber, and thus,recovering the valuable metals contained in the waste.

2. The method of recovering valuable metals from waste according to claim 1, wherein the temperature condition applied to the industrial wastes is in the range of 500° C. for 20 minute or more and 1000° C. for about 10 minutes.

3. The method of recovering valuable metals from waste according to claim 1, wherein the temperature condition applied to the industrial wastes is in the range of 750° C. for 30 minute or more and 1000° C. for about 10 minutes.