CN111718023A

CN111718023A - Method for treating cyanide through catalytic oxidation of iron oxyhydroxide

Info

Publication number: CN111718023A
Application number: CN201911344411.1A
Authority: CN
Inventors: 文树龙
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2020-09-29

Abstract

The invention discloses a method for treating cyanide by catalytic oxidation of iron oxyhydroxide, which comprises the following steps: automatically flowing the wastewater into an oxidation pond, adjusting the pH to 8-12 by adopting sodium hydroxide, and then sequentially adding calcium hypochlorite and a catalyst (calcium hydroxide-iron oxyhydroxide) into the oxidation pond for full reaction; then the supernatant flows into a coagulation tank and a sedimentation tank which are added with polyacrylamide for coagulation sedimentation, and the supernatant is discharged into an adjusting tank and is detected whether the supernatant reaches the standard or not; and the precipitate flows back to the oxidation pond to recycle the catalyst. According to the method, calcium hydroxide-iron oxyhydroxide is used for accelerating the conversion of hypochlorous acid into free oxygen to accelerate the reaction of the free oxygen and cyanide, and the adsorption effect of calcium hydroxide is used for capturing the cyanide and the catalyst, so that the collision probability of the cyanide and the free oxygen is increased, the cyanide breaking reaction is accelerated, the cyanide is oxidized finally, the catalyst is recycled to an oxidation pond for reuse, only a small amount of catalyst lost in the operation process needs to be supplemented, and the wastewater treatment cost is reduced.

Description

Method for treating cyanide through catalytic oxidation of iron oxyhydroxide

Technical Field

The invention relates to the technical field of environment-friendly wastewater treatment, in particular to a method for treating cyanide-containing electroplating wastewater.

Background

In recent years, the problem of cyanide pollution has become serious, and the problem has become one of the problems to be solved urgently in environmental protection. Cyanide is a substance containing cyano (-C is equivalent to N) in a compound molecule, can cause great harm to human beings and livestock, and belongs to a dangerous and highly toxic substance strictly controlled by the state. Cyanide in water can be divided into free cyanide and complex cyanide. The free cyanide is mainly the salt of alkali metal, such as sodium cyanide and potassium cyanide. The main reason for the complex cyanide is that cyano is a strong complexing agent, and forms a stable complex anion in aqueous solution after being complexed with various metals. Cyano is mainly used as a complexing agent in mine mining and precious metal smelting, and therefore, the generated wastewater is mainly complex wastewater containing heavy metals and cyano. Due to the rapid development of the modern industrial and mining industry, more and more wastewater of the type is generated. Therefore, it is very important to research the low-carbon and environment-friendly method for treating cyanide.

At present, a plurality of methods for processing cyanide are available, such as a physical and chemical precipitation method, a membrane absorption method, a Fenton reagent oxidation method, a biological method, a photocatalytic method, an electrochemical method and the like. Although these methods have some effect on cyanide treatment, they have many disadvantages, such as the addition of large amounts of chemical agents and poor treatment effect; the problems that the efficiency of photocatalysis is low and the like caused by easy recombination of photoproduction holes and photoproduction electrons can occur in single photocatalysis. In the process of degrading pollutants in water, the electrochemical method and the photocatalytic method are more advantageous than independent electrochemistry and photocatalysis, and due to the synergistic effect of photocatalysis and electrochemistry, the photon efficiency is improved, the degradation of cyanide is realized, and free heavy metal can be recovered (Zhang optimism, 2006). The photoelectricity-concerted catalytic oxidation technology can effectively separate photoproduction electrons and photoproduction holes, but the utilization of visible light is not improved (Zhao hui min et al, 2007). Most of the currently researched photocatalytic film electrodes must utilize ultraviolet light with high energy, and a large amount of energy, energy and material resources are consumed when the photocatalytic film electrodes are applied to practical engineering.

Therefore, the process with simple development and operation, low energy consumption and low running cost is the process for treating the electroplating cyanide-containing wastewater, which is a problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a method for treating cyanide-containing electroplating wastewater by catalyzing hypochlorous acid with calcium hydroxide-iron oxyhydroxide so as to solve the problems of slow reaction, incomplete complex breaking and large waste residue in the prior art.

The invention achieves the purpose through the following technical scheme:

a method for treating cyanide-containing electroplating wastewater comprises the following steps:

(1) after wastewater automatically flows into an oxidation pond, adjusting the pH value to 7.5-12 by using sodium hydroxide, uniformly mixing quantitative calcium hypochlorite into the wastewater in the oxidation pond, adding a catalyst (calcium hydroxide-nickel oxyhydroxide) into the oxidation pond, and starting a stirring device to perform full reaction;

(2) and (2) enabling the wastewater in the step (1) to flow into a coagulation tank, adding Polyacrylamide (PAM) as a flocculating agent into the coagulation tank, and starting a stirrer to stir.

(3) Opening a valve to enable the wastewater in the step (2) to automatically flow into a sedimentation tank for solid-liquid separation, and refluxing sediment into the oxidation tank in the step (1) after 3 hours of sedimentation; and discharging the supernatant into an adjusting tank.

(4) And (4) adding sulfuric acid to adjust the pH value of the supernatant reacted in the step (3) to 8-9 in an adjusting tank, and discharging the supernatant after the water quality of the supernatant reaches the standard.

Furthermore, the addition amount of calcium hypochlorite in the step (1) is 0.8-2.0 kg per ton of wastewater, the addition amount of calcium hydroxide-nickel oxyhydroxide is 0.5-1.0 mol per liter of wastewater, the oxidation time is 4 hours, and the stirring speed is 150r/min, so that the calcium hydroxide-iron oxyhydroxide is added in the step (2) to enable the nickel oxyhydroxide to promote the decomposition of hypochlorite, the content of free oxygen in a water body is increased, and the calcium hydroxide in the calcium hydroxide-nickel oxyhydroxide can simultaneously adsorb cyanide, so that the collision probability of the free oxygen and the cyanide in the wastewater is increased, and the cyanide breaking efficiency and speed are improved.

Further, the stirring and staying time of the wastewater in the coagulation tank in the step (3) is 15-20 min; the coagulation tank is divided into two grids, the first grid is a fast mixing tank, the rotating speed is controlled at 300r/min, the second grid is a slow mixing tank, the rotating speed is controlled at 50r/min, and dispersed colloidal particles in the wastewater are flocculated into larger particles through the action of a flocculating agent and then automatically flow into the slow mixing tank through the fast mixing tank. Therefore, the rotating speed of the rapid mixing tank is controlled at 300r/min, so that the wastewater is rapidly mixed and reacted with the precipitate and PAM in the rapid mixing tank, and under the rapid stirring action, the stability of the particles is damaged, so that the probability of collision between the particles is increased; and (3) flocculating the fine and dispersed colloidal particles in the wastewater into larger particles by using the PAM polymeric flocculant through adsorption bridging and net catching rolling sweeping effects so as to facilitate solid-liquid separation in the step (4), enabling the wastewater to automatically flow into the slow mixing tank after the large particles are formed, controlling the rotating speed of the stirrer to be 50r/min so as not to damage the large particles, and continuously keeping the small particles to be coagulated into the large particles.

Furthermore, the adding amount of the polyacrylamide is 5-15 g per ton of wastewater.

Further, the surface load of the sedimentation tank in the step (4) is 1.8m³/(m²× h), the retention time is 2 hours, the generated sediment of the sedimentation tank is mainly the catalyst added in the early stage, the sediment flows back to the oxidation tank after being settled, so that the sediment is recycled, part of the sediment flows back to the first sedimentation tank periodically, so that the removed copper is fully recycled, the copper of the whole system can be recycled, the step of treating the sediment by other chemical oxidation methods is eliminated, and the wastewater treatment cost is greatly reduced.

Further, the oxidation pond needs to be covered and sealed in the step (2).

The method for treating the electroplating cyanide-containing wastewater provided by the invention has the following beneficial effects:

(1) calcium hydroxide-iron oxyhydroxide is used for catalysis, so that hypochlorous acid can be accelerated to be converted into free radicals, a large amount of free oxygen is generated, the content of the free oxygen in a water body is increased, calcium hydroxide and ferrous hydroxide/iron hydroxide in the calcium hydroxide/iron oxyhydroxide can adsorb cyanide at the same time, the collision probability of the free oxygen and the cyanide is increased, the cyanide breaking speed and effect are improved, and meanwhile, the calcium hydroxide is beneficial to the subsequent coagulation reaction and the recycling of a catalyst;

(2) the sediment in the coagulation tank flows back to the oxidation tank, so that the waste of the catalyst is reduced, and the utilization rate of the catalyst is increased;

(3) the reactor for treating the electroplating cyanide-containing wastewater by catalyzing calcium hypochlorite to oxidize by using the calcium hydroxide-iron oxyhydroxide has the advantages of simple structure, low engineering cost, simple and convenient operation and low operating cost, and is favorable for popularization and application.

Drawings

FIG. 1 is a schematic flow chart of one embodiment of the method for treating cyanide-containing electroplating wastewater according to the invention.

Detailed Description

The idea of the invention is explained in further detail below with reference to the figures and examples.

As shown in figure 1, the method for treating the electroplating cyanide-containing wastewater comprises the following steps:

(1) after wastewater automatically flows into an oxidation pond, adjusting the pH value to 8-12 by using sodium hydroxide, uniformly mixing quantitative calcium hypochlorite into the wastewater in the oxidation pond, adding a catalyst (calcium hydroxide-nickel oxyhydroxide) into the oxidation pond, and starting a stirring device to perform full reaction;

Example 1

The cyanide-containing wastewater from a certain factory in Zhongshan mountain is treated, the water quality of raw water is 20.45mg/L of cyanide, the pH value is 3.0, and the Chemical Oxygen Demand (COD) is 1297.36 mg/L.

Adding raw electroplating wastewater into a first sedimentation tank, adding sodium hydroxide to adjust the pH value to 7.5, reacting for 4 hours, automatically flowing the wastewater into an oxidation tank, adjusting the pH value to 8, adding 0.8 kg of calcium hypochlorite into the oxidation tank according to each ton of wastewater, adding 0.2mol of calcium hydroxide-iron oxyhydroxide into each liter of wastewater, and reacting for 3 hours; after the reaction, the mixed solution automatically flows into a coagulation tank, 5g of PAM is added into each ton of wastewater for coagulation, then a stirrer is started to start stirring, and the retention time of the wastewater in the coagulation tank is 15min (the retention time of a fast mixing tank is 5min, the rotating speed is 300 r/min; the retention time of a slow mixing tank is 10min, and the rotating speed is 300 r/min); and (3) enabling the effluent after the reaction to flow into a second sedimentation tank for solid-liquid separation, wherein the retention time is 2 hours, enabling most of precipitates to flow back into the oxidation tank, enabling a small part of precipitates to flow back to a raw water port and then enter the first sedimentation tank for recycling, discharging the supernatant into an adjusting tank, and adjusting the pH to be 8. And repeating the test for three times, wherein the average concentration of total cyanogen in the final supernatant water sample is 0.38mg/L, the average concentration of COD is 48.59mg/L, the water quality of the effluent of the total cyanogen reaches the effluent quality standard in Table 3 in the emission Standard of electroplating pollutants (GB 21900-2008), and the treatment effect is good.

Claims

1. A method for treating cyanide under the catalysis of iron oxyhydroxide is characterized by comprising the following steps:

(1) automatically flowing the wastewater into an oxidation pond, adjusting the pH value to 7.5-12 by adopting sodium hydroxide, uniformly mixing quantitative calcium hypochlorite into the wastewater in the oxidation pond, adding a catalyst (calcium hydroxide-iron oxyhydroxide) into the oxidation pond, and starting a stirring device to perform full reaction;

(2) enabling the wastewater in the step (1) to flow into a coagulation tank, adding Polyacrylamide (PAM) serving as a flocculating agent into the coagulation tank, and starting a stirrer to start stirring;

(3) opening a valve to enable the wastewater in the step (1) to flow into a second sedimentation tank for solid-liquid separation, after 3 hours of sedimentation, enabling sediment (including a large amount of catalyst) to flow back into the oxidation tank in the step (1), and discharging supernatant into an adjusting tank;

2. The method of claim 1, wherein the cyanide is oxidized by the ferric hydroxide catalyst,

in the step (1), the addition amount of the calcium hypochlorite is 0.8-2.0 kg per ton of wastewater, the addition amount of the catalyst (calcium hydroxide-iron oxyhydroxide) is 0.5-1.0 mol per liter of wastewater, the oxidation time is 4 hours, and the stirring speed is 150 r/min.

3. The method for treating cyanide under the catalysis of iron oxyhydroxide according to claim 1, wherein the stirring residence time of the wastewater in the coagulation basin in the step (2) is 15-20 min; the coagulation tank is divided into two grids, the first grid is a fast mixing tank, the rotating speed is controlled at 300r/min, the second grid is a slow mixing tank, the rotating speed is controlled at 50r/min, and the colloidal particles dispersed in the wastewater form larger particles through the flocculation effect of the flocculating agent and then automatically flow into the slow mixing tank through the fast mixing tank.

4. The method as claimed in claim 1, wherein the amount of polyacrylamide added in step (3) is 5-15 g/ton of wastewater.

5. The method as claimed in claim 1, wherein the surface load of the sedimentation tank in the step (4) is 1.8m³/(m²× h), the residence time was 2 hours.

6. The method as claimed in claim 1, wherein the oxidation pond is sealed by a cover in the step (2).