JP2013181893A - Method for detecting nickel contained in drain water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for instantaneously detecting nickel leakage to drain water by continuously measuring suspended matter concentration (SS concentration) of drain water filtered after neutralization sedimentation treatment and turbidity of drain water obtained by pH adjusting the drain water with sulfuric acid in a drain water treatment process for sedimenting nickel in waste water containing nickel by neutralization sediment treatment.SOLUTION: A method for detecting nickel in waste liquid detects the existence of nickel in drain water by continuously measuring suspended matter concentration (SS concentration) of the drain water filtered after neutralization sedimentation treatment in a drain water treatment process for sedimenting nickel in waste water containing nickel by the neutralization sedimentation treatment using alkali, and turbidity of waste water obtained by pH adjusting the drain water with sulfuric acid.

Description

  The present invention continuously monitors the suspended solids concentration (suspended solids concentration, hereinafter referred to as SS concentration) and turbidity of wastewater-treated water in a wastewater treatment process in which sewage containing heavy metals is neutralized with slaked lime. Therefore, the present invention relates to a method for detecting nickel leakage into waste water and preventing outflow into the sea area.

  Sewage discharged from the electric nickel production process and nickel sulfate production process contains heavy metal components such as nickel, cobalt, iron, and zinc, and these heavy metal components are neutralized by slaked lime in the wastewater treatment process. The separation and removal method is used.

  The principle of removal is to add slaked lime slurry to sewage containing heavy metals and form a neutralized starch by keeping it in a highly alkaline region, and then capture and separate the neutralized starch with a filter press that serves as a filter. The filtrate, which is the residual liquid, is adjusted to a neutral region with sulfuric acid, mixed with other general waste water cooling water and domestic waste water, and sent to the oil / water separation tank.

The reason why such an oil-water separation tank is used is that the sewage drained from nickel hydrometallurgy also includes sewage from the solvent extraction process that separates nickel and cobalt. It is intended to detect the oil content through an oil-water separation tank. In addition, an automatic analyzer that measures the nickel concentration in the sewage is installed in the oil / water separation tank, and if it exceeds a certain concentration, it is discharged from the oil / water separation tank to a disposal site (for example, sea area) by automatic control. This system has a system that prevents the discharge to the natural world such as the sea area by stopping the discharge pump, and starting the recovery pump instead to feed water to a large emergency recovery tank.
In addition, the system is similarly linked when a predetermined control concentration is exceeded in the pH and COD (UV meter) values.

  In this way, the sewage that has passed through the wastewater treatment process is once passed through the oil / water separation tank, mixed with cooling water and domestic wastewater that are general wastewater, and then discharged into the sea area by pumping up, It is necessary to check and monitor for nickel leakage. Since the method of measuring nickel concentration by ordinary chemical analysis takes time and labor, an apparatus for automatically measuring nickel concentration has been developed (see, for example, Patent Document 1).

However, the nickel automatic analyzer installed in the oil / water separation tank has a measurement frequency of about 20 minutes per measurement. Therefore, if sewage containing nickel leaks during the 20 minutes, the sea area depends on the detection timing. There is a risk of being released to
The assumed risk is that when a high concentration nickel stock solution flows into the wastewater treatment process, the high concentration nickel flows out as wastewater treatment water when passing through the filter press in a state where the neutralization reaction is not completed. In addition, there are cases where the neutralized slurry leaks due to breakage or deterioration of the filter cloth of the filter press, and nickel is re-eluted in the pH adjustment step with sulfuric acid later.
Therefore, in order to prevent such nickel outflow, there has been a demand for a method of instantaneously detecting nickel leakage in water after wastewater treatment to prevent leakage into the sea area.

JP 2004-611165 A

  The present invention relates to a wastewater treatment process in which nickel is precipitated by neutralizing and precipitating sewage containing nickel, and the suspended solid concentration (SS concentration) of the wastewater filtered after the neutralizing and precipitating treatment and the wastewater whose pH is adjusted with sulfuric acid. The purpose is to provide a method for instantaneously detecting nickel leakage into the waste water by continuously measuring the turbidity of the water.

  In view of such a problem, as a result of earnest investigation and research, the first invention of the present invention is to filter the sewage containing nickel after the neutralization precipitation process in the wastewater treatment process in which nickel is precipitated by the neutralization precipitation process using alkali. By continuously measuring the suspended solids concentration (hereinafter referred to as SS concentration) of wastewater and the turbidity of wastewater whose pH was adjusted with sulfuric acid, the presence of nickel in the wastewater filtered after neutralization precipitation treatment was confirmed. It is the nickel detection method in the waste_water | drain characterized by detecting.

  In the second invention of the present invention, the continuous measurement of suspended solids concentration (SS concentration) in the first invention is carried out by the suspended matter concentration meter (hereinafter referred to as SS) This is a method for detecting nickel in wastewater, which is performed by installing a densitometer.

  In the third invention of the present invention, the continuous measurement of turbidity in the first and second inventions is carried out by installing a turbidimeter on the waste liquid outflow side of the pH adjusting tank for adjusting the pH of the wastewater with sulfuric acid. A method for detecting nickel in wastewater.

  According to the present invention, in the wastewater treatment step of precipitating nickel by neutralization precipitation using alkali such as slaked lime with sewage containing nickel, the SS concentration of the wastewater filtered after the neutralization precipitation treatment, and the wastewater whose SS concentration was measured By continuously measuring the turbidity of waste liquid adjusted to pH with sulfuric acid, the nickel concentration in the waste water can be continuously monitored, and it is possible to prevent the waste liquid containing nickel from flowing out into the natural environment such as the sea area. It is what.

It is a figure which shows the pH adjustment tank provided with SS concentration meter and turbidity meter used in the Example, (a) is an external appearance photograph, (b) is a photograph which shows the internal structure of a pH adjustment tank. It is a figure which shows a SS density | concentration detection result when the wastewater starch slurry equivalent to 25 mg / L is thrown into F / P filtrate. It is a figure which shows the turbidity value transition measurement result at the time of nickel concentration change.

Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, in a wastewater treatment process in which nickel-containing wastewater is subjected to neutralization precipitation treatment with alkali such as slaked lime, and nickel is precipitated, the SS concentration of the wastewater filtered after the neutralization precipitation treatment and pH adjustment of the wastewater with sulfuric acid By continuously measuring both of the turbidity of the waste liquid, it is possible to continuously monitor nickel and detect abnormalities in the wastewater.

  In general wastewater treatment, nickel is precipitated by neutralization precipitation treatment in which alkali such as slaked lime is added to sewage, and filtered by a filter such as a filter press to separate wastewater treatment starch containing nickel as a precipitate. To the filtrate from which the wastewater-treated starch has been separated, sulfuric acid is added to adjust the pH to neutral, and after mixing with general wastewater, it is discharged as wastewater through an oil-water separation tank.

The nickel grade in the wastewater-treated starch is about 1 to 5%, and if this leaks from the filter press (filter) due to some event, the starch is adjusted in the pH adjustment step to adjust to the neutral region by adding sulfuric acid later. Part of the object is dissolved. That is, nickel contained in the wastewater starch is eluted again and released into the natural world (for example, the sea area).
As means for preventing this, the SS concentration in the water flow through the filter press is continuously measured to monitor the behavior of the filter press and detect the abnormality. That is, it detects nickel elution.

  Therefore, it is desirable that the SS densitometer used in the present invention can be sampled in a short period, and it is desirable that measurement can be performed in at least one minute period. Sampling in a short cycle enables instantaneous judgment. Even when using multiple filter presses, it is possible to instantly determine the anomaly by measuring each filter press instead of the collected water. it can.

Moreover, since SS density | concentration measures SS density | concentration containing the nickel which leaks from a filter press, it is necessary to measure the water flow of a filter press. For this reason, the SS densitometer is installed on the line after the filter press. In order to further shorten the determination time, it is desirable that the SS densitometer be closer to the filter press. Moreover, if it enters into the pH adjustment tank which adjusts pH with a sulfuric acid, since suspended | floating matter (SS) melt | dissolves and it will no longer be detected, it is unpreferable.
Therefore, the SS densitometer is preferably installed on the filter press filtrate inflow side of the pH adjustment tank.

In addition, turbidity that continuously measures the turbidity in wastewater to detect wastewater that contains nickel but does not contain suspended solids (SS) but prevents nickel leakage by targeting pH-treated wastewater A measurement process is performed.
This turbidity is measured, for example, when a nickel stock solution (nickel concentration of about 100 g / L) supplied by nickel electrolysis is sent to the wastewater treatment process due to some event. If it passes, the high-concentration nickel leaks, and in the detection by the SS concentration performed in the previous SS concentration measurement, there is no SS leak if the filter press is in a normal state. The detection of nickel is difficult.
Therefore, in this process, the principle of the infrared scattered light detection method of the turbidimeter is used to detect nickel leakage using the fact that the measured value decreases due to the decrease in transmitted scattered light when high concentration nickel leaks. To do.

The turbidimeter to be used measures the re-dissolved slurry containing nickel flowing into the pH adjusting tank. Therefore, it is necessary to install the turbidimeter after the pH adjustment tank, and it is desirable to install it on the waste liquid outflow side of the pH adjustment tank in order to detect it quickly.
The turbidity rapidly increases as nickel flows in, and then decreases as the nickel concentration increases. This is because light hardly scatters in the absence of particles, and the turbidity in the liquid tends to be negative when the nickel concentration increases beyond a certain concentration.

  The present invention will be further described below using examples.

FIG. 1 shows a pH adjustment tank 1 for testing used in the examples. (A) is an external view photograph, (b) is a photograph which shows the internal structure of a tank (dedicated basket) by removing the tank lid.
The tank capacity of the pH adjusting tank 1 in FIG. 1 is 94 L, and the inside of the dedicated tub 10 is attached with a weir plate 11 and a gap is formed in the lower part so that bubbles in the liquid do not directly touch the detection unit. This prevented the entrapment of bubbles and the retention of suspended solids (SS). The direction indicated by the black arrow indicates the direction in which drainage flows. In addition, the pH is adjusted with sulfuric acid in the dedicated dredger 10, and the SS concentration meter 2 is installed in the drainage inflow portion 12 partitioned by the weir plate 11 so as not to be affected by the dedicated dredger 10. The turbidimeter 3 is installed in the partitioned waste liquid outflow portion 13.
An SS densitometer 2 (manufactured by Toa DKK Co., Ltd .: SSD-10) that measures the SS concentration is installed on the inflow side (drainage inflow section 12) before the pH is adjusted with sulfuric acid, and the turbidimeter 3 (HACK) (SOLITAX) was installed on the waste liquid outflow side (waste liquid outflow part 13).

Next, assuming that wastewater containing starch was mixed, wastewater starch slurry having an SS concentration of 25 mg / L was charged into the pH adjustment tank of FIG.
The flow rate was set to two levels of 15 L / min and 20 L / min, simulated waste water was flowed at the flow rate, and the SS concentration threshold was set to 2 mg / L to detect wastewater starch.

FIG. 2 shows the SS concentration detection result when drained starch slurry is added as a filter press filtrate.
When the flow rate was 15 L / min, an increase in SS concentration was detected after 7 minutes and at 20 L / min after 5 minutes, and it was found that the outflow of suspended solids (SS) could be suppressed to a very small amount.

Next, assuming that the suspended matter (SS) is dissolved by sulfuric acid and becomes wastewater containing nickel, drainage water whose nickel concentration is changed from 5 mg / L to 100 mg / L is passed through, and the turbidity is obtained. The degree was measured.
A predetermined amount of NiCl ₂ solution was added to general water to prepare a simulated waste water adjusted to a predetermined nickel concentration, and the detection state of turbidity when water was passed was confirmed.

FIG. 3 shows the turbidity value transition measurement results when the nickel concentration changes.
From FIG. 3, when nickel waste liquid flows in, turbidity rose rapidly within 2 minutes. Thus, it can be seen that the dissolved nickel can be detected in a short time by measuring the turbidity. Further, since turbidity varies depending on nickel concentration, it is possible to obtain an approximate nickel outflow amount from the measured value of turbidity by grasping the relationship between turbidity and nickel concentration in advance.

(Comparative Example 1)
An automatic nickel concentration measuring apparatus as disclosed in Patent Document 1 was installed on the outflow side of the waste liquid, and the same simulated waste liquid as in Example 1 was flowed to measure the nickel concentration.
As a result, it took 20 minutes to detect nickel, and during that period, it was confirmed that the waste liquid containing nickel was discharged.

1 pH adjustment tank 2 Suspended substance concentration meter (SS concentration meter)
3 Turbidimeter 10 Dedicated basin 11 Dam plate 12 Drainage inlet 13 Wastewater outlet

Claims (3)

  The suspended solids concentration (hereinafter referred to as the SS concentration) of the wastewater filtered after the neutralization precipitation treatment in the wastewater treatment step in which nickel is precipitated by neutralization precipitation treatment using alkali in the wastewater containing nickel, and the wastewater is treated with sulfuric acid. A method for detecting nickel in wastewater, characterized in that the presence of nickel in the wastewater is detected by continuously measuring the turbidity of the waste liquid pH-adjusted in step (1).   Continuous measurement of the suspended matter concentration (SS concentration) is performed by installing a suspended matter concentration meter (hereinafter referred to as an SS concentration meter) on the wastewater inflow side of a pH adjustment tank that adjusts the pH of the wastewater with sulfuric acid. The method for detecting nickel in wastewater according to claim 1.   The nickel in the wastewater according to claim 1 or 2, wherein the continuous measurement of the turbidity is performed by installing a turbidimeter on a waste liquid outflow side of a pH adjustment tank for adjusting the pH of the wastewater with sulfuric acid. Detection method.