JPS6020077B2 - Method for treating sludge containing calcium fluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waste treatment method, and particularly to a method for detoxifying sludge containing calcium fluoride.

Fluorine compounds are used in semiconductor manufacturing processes and plating operations, but the wastewater after treatment contains fluorine as well as harmful substances such as chromium and zinc.

In order to render this waste harmless, calcium such as slaked lime or limestone is usually added, fluorine is converted into calcium fluoride, and heavy metals such as chromium and zinc are converted into hydroxides, which are precipitated and separated to be discharged as harmless wastewater. The generated precipitate (sludge) contains calcium fluoride and calcium salts from the reaction, as well as hydroxides of various components.
It is difficult to recycle effectively, and since it is a slurry containing around 70% water, it is difficult to dump it outdoors.Currently, the bits are dug up and stored, but the increasing amount of waste makes it difficult to dispose of them. I got used to it. A high-temperature firing process is a method for detoxifying sludge containing calcium fluoride. This method involves burning the above sludge at a pressure of 1,000 qo or more, which makes it possible to reduce the amount of sludge to a large extent, and also to reduce the amount of harmful substances such as fluorine and chromium dissolved in water (elution) from the raw sludge from the feeder. It can be lowered to large compared to . However, depending on the processing conditions, hexavalent chromium may be eluted from the aggregates formed by the above method. For this reason, additives such as clay are mixed with the sludge and fired to stabilize the chromium as a spinel structure (M○・Cr203). This method has the disadvantage that the amount of sintered bodies increases because 10% or more of additives are mixed into the sludge.
The purpose of the present invention is to add a small amount of additives when calcining sludge containing calcium fluoride.
The objective is to obtain a harmless sintered body. The present invention is a sintering method that reduces the release of hexavalent chromium from competitive mackerel by mixing a reducing agent made of hydroxylamine sulfate with sludge containing calcium fluoride and firing it for 1,000 to 1,200 hours. The purpose is to provide a method. That is, according to experiments, the sludge containing calcium fluoride was
A good composite can be obtained by firing with 100 pieces, but at this time, if the concentration of iron in the sludge increases,
It was revealed that the elution of hexavalent chromium from the dawn stripes increased.

This means that when the sludge is heated, the iron in the sludge becomes Fe.
203, but when it reaches 105,000 or more, the following reaction produces Fe304, which is extremely stable as an iron oxide, and chemically active oxygen.

Furthermore, it is thought that this oxygen reacts with chromium in the sludge in the following manner to produce one Cr2033(0) 36-valent chromium.

Here, in order to make the iron in the sludge exist as Fe304 at a relatively low temperature, when the sludge and hydroxylamine sulfate, which is a reducing agent for iron, are mixed, the iron in the sludge becomes Fe304.
It is retained as (OH)2, and when heated, Fe20
Fe304 is generated without passing through 3, and no oxygen is generated even at 1050 qo or more, so hexavalent chromium is not generated either.

This will be explained below using examples. Sludge A containing calcium fluoride with 70% water content (after removing water, the main components are 20% calcium fluoride, 22% magnesium oxide)
0%, calcium phosphate 15%, calcium oxide 10%
), this sludge mixed with 5% ferric hydroxide B, and the sludge B mixed with 3% hydroxylamine sulfate C were heated at a firing temperature of 1000 to 110°C.
The figure shows the change in elution amount when firing in the range of 0°C.

Here, the elution amount of hexavalent chromium is 10 times the sintered body and 100 times the pure water.
This is the concentration in the furnace solution after stirring for 6 hours in the upper part of the furnace.
In sample A, the amount of hexavalent chromium eluted is small at any firing temperature, and there is no problem.

In sample B, since 5% of Fe(OH)3 was added, the hexavalent chromium content was around 4 ppm at a firing temperature of around 1050°C, significantly exceeding the 1.5 ppm criterion for hazardous industrial waste. Furthermore, in sample C, by adding 3% hydroxylamine sulfate, the firing temperature was increased to 105020.
Even in the vicinity, it is below lppm, satisfying the standard value,
It can be seen that hydroxylamine sulfate is effective in reducing chromium elution. According to the present invention, when calcining sludge containing calcium fluoride, in order to prevent the elution of hexavalent chromium from the dawn stripes, additives such as clay are mixed in at least 10% in the conventional method. By mixing small amounts of additives, it became possible to obtain high quality Akatsuki mackerel.

[Brief explanation of the drawing]

A diagram showing the relationship between firing temperature and hexavalent chromium.

Claims (1)

[Claims] 1 When sludge containing calcium fluoride, chromium, and trivalent iron is treated at high temperature, hydroxylamine sulfate is added to the sludge to keep the iron divalent, and then 10
A method for treating sludge containing calcium fluoride, which comprises firing at a temperature of 00 to 1200°C.