JPS60248288A - Treatment of waste water from mine - Google Patents

Abstract

PURPOSE:To render the waste water from mines harmless by allowing magnesium hydroxide and other alkalis to react with the waste water from mines contg. heavy metals. CONSTITUTION:Magnesium hydroxide and other alkalis such as slaked lime and calcium carbonate are allowed to react with the acidic waste water from mines contg. heavy metals such as copper and arsenic, and the heavy metals are precipitated as hydroxides and removed. The waste water is simultaneously neutralized. The strongly acidic waste water from mines contg. heavy metals can be made harmless in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating mine drainage, particularly a method for detoxifying strongly acidic mine drainage containing heavy metals.

A considerable amount of wastewater is always discharged from mines, especially from abandoned mines, and this contains many harmful heavy metals such as iron, manganese, zinc, cadmium, copper, lead, and chromium in the form of sulfates. Contained in relatively large amounts in many species. From an environmental point of view, discharging all of these wastewater as is is not deceiving, and is a heavy waste! 4 must be removed so that the F value is below the standard value, and the wastewater must also be neutralized.

Conventionally, such means include a method in which slaked lime is used alone to precipitate and remove heavy metals as hydroxides and neutralized, or a method in which slaked lime is used together with calcium carbonate as a 1gl1 regulating agent and a settling aid for p'. It has been done and is being done again.

However, these methods produce a large amount of gypsum as a by-product as long as a calcium-based treatment agent is used, since most of the mine drainage contains a large amount of sulfate radicals as an acid source. Although gypsum itself is harmless, releasing it into the water causes problems every day, and it significantly exceeds environmental standards, which is unacceptable.

For this reason, it is necessary to separate the gypsum using a filter or the like, but gypsum has a high moisture content (85 to 90%) and requires a huge amount of processing capacity, making it difficult to handle.

The sound of the present invention eliminates such drawbacks, effectively separates heavy metals from wastewater by sedimentation, effectively neutralizes sulfuric acid radicals, and does not cause secondary pollution caused by related organisms. We have previously proposed a method of employing magnesium hydroxide as a sedimentation agent and a neutralizing agent for wastewater. Although this is a means that can sufficiently achieve the intended purpose, the present invention has been further investigated and found that when other alkalis are used together with magnesium hydroxide, the sedimentation rate of heavy metals increases, and the obtained It has been found that the water content of the sediment is relatively small, making dehydration easier.

Thus, the present invention is characterized in that magnesium hydroxide and other alkalis are used in combination with acidic mine drainage containing heavy metals, and the heavy metals are precipitated and removed as hydroxides, and the drainage is neutralized. The purpose of the present invention is to provide a method for treating mine wastewater.

In the present invention, the heavy metal II4 contained in mine drainage is ionized in an acidic solution, and can be treated with any substance that produces hydroxide precipitates in neutral to alkaline conditions. Such heavy metals include, for example, copper, arsenic, iron, zinc, manganese, cadmium, lead, mercury,
Examples include chromium and nickel.

In addition, most of the acidic mine drainage is caused by sulfate radicals, but there is no problem even if other acids are mixed in.

The amount of magnesium hydroxide used for such wastewater is strictly determined by the W1 class heavy metals contained in the wastewater and the degree of acidity, but generally it is 90% of the alkali equivalent required to neutralize the wastewater. It is best to adopt ~50%. If the amount used is less than the above range, the heavy metal hydroxide precipitate produced will be poorly compacted and the water content will be high, increasing the amount of precipitate produced.Therefore, there is no particular limitation on the preferred mode of use of 9° magnesium hydroxide. , a dried product or a product obtained in the form of a slurry, such as a seawater mug, can be used as is.

Examples of alkali used in combination include slaked lime, calcium carbonate, calcium oxide, sodium hydroxide, sodium carbonate, and sodium bicarbonate, and one or more of these may be used as appropriate. However, when the concentration of sulfate radicals in wastewater is high, calcium alkalis such as slaked lime and calcium carbonate produce poorly soluble gypsum precipitate as a by-product, increasing the amount of precipitate. Sodium alkali is preferred.

The appropriate amount of these alkalis to be used is 10 to 50% of the total amount of alkalis required to neutralize the waste water.

If it deviates from the above range, it is not preferable because the desirable sedimentation properties and low water content of heavy metal hydroxides, which are the objectives of the present invention, may not be effectively achieved.

Regarding the method of adding magnesium hydroxide and other alkalis to the wastewater, it is preferable to add and react magnesium hydroxide at the same time as the alkali to be used together, or to add and react magnesium hydroxide after adding and reacting the alkali to be used in combination. . If an alkali used in combination is added and reacted after magnesium hydroxide is added, the effect of using magnesium hydroxide may not be sufficiently obtained, which is not preferable.

When the method of the present invention is adopted, the precipitation of heavy metal hydroxides progresses substantially completely in a short period of time, and when the heavy metal hydroxides are filtered, the water content can be reduced to 70% or less. is also relatively easy. In addition, sulfate radicals react with magnesium to produce magnesium sulfate, but due to its high solubility, it does not form as a precipitate in normal mine drainage treatment, and since it is pot-free, It has the advantage that it can be immediately discharged.

Next, the present invention will be explained by examples.

Example 1 Contains as heavy metals copper 15 pI)m, iron 501)1)m, zinc 61)l)m, and furthermore aluminum 41 pp
Mine drainage water with a pH of 2.7 containing 850 ppm of sulfate roots 5
! 6 g of magnesium hydroxide x (corresponding to 80% of the alkali equivalent required for neutralization) and 0.5 g of slaked lime (corresponding to 20% of the alkali equivalent required for neutralization) were simultaneously added as a 10% slurry liquid.

After adding the alkali, the mixture was stirred for 40 minutes and the resulting precipitate was completely condensed.

The results of analyzing the raised liquid are shown in Figure 1. In addition, the entire amount of the generated precipitate was filtered at a gauge pressure of 3 K9/cm2 using a small filter press filtration machine with a filtration area of 20 x 2 using a filter cloth with an air permeability of 50 crA/Qm2 minutes atm. The amount of cake remaining was 8.3 g, and the moisture content of this cake was 68%.

Table 1 Example 2 Mine drainage used in Example 15. 1/l of magnesium hydroxide. o g (50% of the alkali equivalent required for neutralization)
) and slaked lime 1. a g (equivalent to 50 g of alkali equivalent for neutralization) was added as a 10% slurry liquid at the same time, and using the same equipment as in Example 1, the wastewater was treated and the precipitate was filtered in the same manner. .

Table 2 shows the analysis results of the supernatant. The amount of cake after filtration was 9.0 g, and the moisture content of this cake was 69 g.

Table 2 Example 3 Mine drainage used in Example 1 5! 0.6 g of magnesium hydroxide (equivalent to 30% of the alkali equivalent required for neutralization) and 1.8 g of slaked lime (equivalent to 70 g of the alkali equivalent required for neutralization) were added simultaneously as a 10% slurry solution.
Using the same apparatus as in Example 1, the waste water was treated and the precipitate was filtered in the same manner.

Table 3 shows the analysis results of the supernatant. The cake lid after filtration weighed 9.8 g, and the moisture content of this cake was 69 g.

Table 3 Example 4 Mine drainage used in Example 1 5! , magnesium hydroxide 1. a g (equivalent to 80 yen of the alkali equivalent required for neutralization) and 0.5 g of sodium hydroxide (equivalent to 20 yen of the alkali equivalent required for neutralization) were added simultaneously as 10% solution, using the same apparatus as in Example 1. The wastewater was treated and the precipitate was filtered using the same method.

The analysis results of the supernatant are shown in Table 4VC. The amount of cake after filtration was 8.5 g, and the moisture content of this cake was 68 g.

(9) Table 4 Comparative Example 1 Mine drainage used in Example 1 5! 2.5 g of magnesium hydroxide was added as a 10-thi slurry solution, and the wastewater was treated and the precipitate was filtered in the same manner as in Example using the same equipment. The analysis results of the supernatant liquid are shown in Table 5. It took 65 minutes of agitation and coagulation to achieve the results shown.

The weight of the cake after filtration was 8.0 g, and the moisture content of this cake was 72 g.

Comparative Example 2 Mine drainage used in Example 1 5! Add 2.5g of slaked lime to 10
Add it as a slurry solution, use the same equipment as in Example 1, and treat the wastewater and filter the precipitate in the same manner (:
1+O) Ta. Table 6 shows the analysis results of the supernatant. The amount of cake after filtration was 21.3 g, and the moisture content of this cake was 88%.

Table 5 Table 6 (11)

Claims (5)

[Claims] (1) A mine characterized by reacting magnesium hydroxide with an alkali other than magnesium hydroxide against acidic mine drainage containing heavy metals to precipitate and remove the heavy metals as hydroxides and neutralizing the drainage. How to treat wastewater. (2) The method according to claim (1), wherein the heavy metals are copper, arsenic, iron, zinc, manganese, cadmium, lead, mercury, chromium, and nickel. (3) The method according to claim (1), wherein the acidic mine drainage contains sulfate radicals. (4) The method according to claim (1), wherein the alkali used in combination with magnesium hydroxide is at least one selected from slaked lime, calcium carbonate, calcium oxide, sodium hydroxide, sodium carbonate, and sodium bicarbonate. (5) The amount of alkali used together with magnesium hydroxide is 10 to 50% of the total amount of alkali required to neutralize wastewater.
The method according to claim (1), which is: