abstract

The present invention discloses a wastewater defluorination agent, characterized in that the defluorination agent contains rare earth elements, and the defluorination agent also contains polyacrylamide. The principle of defluorination of the agent described in the present invention belongs to the ion precipitation method for removing fluoride ions. Fluoride ions combine with rare earth element ions to form rare earth fluoride precipitates, which are insoluble in water. Fluoride ions in water are removed through ion co precipitation, thus having good selectivity. The generated rare earth fluoride is recycled for rare earth smelting. Suitable for the removal of low concentration fluoride ion pollution factors in wastewater, its characteristics are good and stable fluoride removal effect, low treatment cost, and recyclable generated rare earth fluoride.

right-claiming document

1. A method for using a fluoride removal agent for wastewater, characterized in that:,

1) The fluorine removal agent contains rare earth elements; The rare earth elements are any one or more of lanthanum, cerium, praseodymium, or neodymium; The rare earth element is at least one of rare earth chloride or rare earth carbonate; The defluorination agent formed by rare earth chloride is an aqueous solution, and rare earth chloride accounts for 1-65% of the total mass of the defluorination agent; The defluorination agent formed by the rare earth carbonate is in powder form, and the proportion of rare earth carbonate in the total mass of the defluorination agent is greater than or equal to 80% and less than 100%; The defluorination agent also contains polyacrylamide, and the amount of polyacrylamide added is 0.1 ‰ -0.2 ‰ in the defluorination agent formed by rare earth chloride, and 0.5 ‰ -1 ‰ in the defluorination agent formed by rare earth carbonate;

2) The preparation method of the fluorine removal agent described:

A. The preparation method of defluorinated agents formed by rare earth chloride is as follows:

(a) Prepare rare earth chloride solution with a mass fraction of 1-65% and mix evenly;

(b) In the rare earth chloride solution described in step (a), a flocculant is added at a ratio of 0.1 ‰ to 0.2 ‰ of the total weight, mixed evenly, and a wastewater defluorination agent mainly composed of rare earth chloride is prepared;

B. The preparation method of a defluorination agent formed by rare earth carbonate is as follows: mix the proportion of rare earth carbonate with polyacrylamide, stir evenly;

3) The steps for using the defluorinated agent are as follows:

A. The usage method of the defluorination agent formed by rare earth chloride: The pH value is controlled at around neutral 7, and the defluorination agent is added according to the mass ratio of fluoride ions to rare earth chloride at 0.24-0.25. The agent is stirred for 30 minutes, fully reacted, and allowed to settle for 60 minutes. After the precipitate is recovered, solid-liquid separation is carried out, which is further used for rare earth smelting;

B. The method of using the defluorination agent formed by rare earth carbonate is as follows: control the pH value at around 2.5, add the defluorination agent of rare earth carbonate according to the mass ratio of fluoride ions to rare earth carbonate of 0.22-0.29, stir for 30 minutes, fully react, and let it settle for 60 minutes. The formed fluorinated rare earth precipitate is recovered and solid-liquid separated for further use in rare earth smelting.

instructions

A method of using a fluoride removal agent for wastewater

technical field 

The present invention relates to the field of fluorine-containing wastewater treatment, particularly to a wastewater defluorination agent and a preparation method mainly composed of rare earth element compounds.

Background technology

Fluorine is one of the essential trace elements for the human body, and the suitable concentration of fluoride in drinking water is 0.5-1.0mg/L. When drinking water lacks fluoride, it is prone to dental caries; However, long-term consumption of water with a fluoride concentration higher than 1.0mg/L can cause dental fluorosis; Long term consumption of water with a fluoride concentration of 3-6mg/L can cause fluorosis. Fluorinated groundwater is widely distributed in China, especially in arid areas of northwest China. About 70 million people drink water with excessive fluoride levels, leading to varying degrees of fluoride poisoning. In industry, wastewater discharged from industries such as fluorine-containing ore mining, metal smelting, aluminum processing, coke, glass, electronics, electroplating, fertilizers, pesticides, etc. often contains high concentrations of fluoride, causing environmental pollution. The research on fluorine removal technology has always been an important topic in the fields of environmental protection and health both domestically and internationally.

Fluorine containing wastewater, currently most domestic production plants do not have complete treatment facilities, and the fluorine content in the discharged wastewater exceeds the national discharge standards, seriously polluting the environment. According to the national comprehensive sewage discharge standard, the fluoride ion concentration should be less than 10mg/L. In some industry standards or special discharge areas, the fluoride ion concentration should be less than 2mg/L. The drinking water standard requires the fluoride ion concentration to be less than 1mg/L. At present, the commonly used fluoride removal agents for wastewater at home and abroad can be roughly divided into two categories, namely calcium salt precipitation method fluoride removal agents and adsorption method fluoride removal agents.

Calcium salts mainly include CaO, CaCl2, Ca (OH) 2, etc. By adding chemical drugs mainly composed of calcium salts, calcium fluoride precipitates are formed or calcium fluoride is adsorbed onto the precipitate formed and precipitated together. This method is simple, easy to handle, and low in cost, but the solubility of lime is low, and can only be added in emulsion. The resulting CaF2 precipitate wraps around the surface of Ca (OH) 2 particles, making it unable to be fully utilized, resulting in a large dosage. The fluoride content in the treated wastewater can generally only decrease to 20-50mg/L, which cannot meet the first level standard specified in the Comprehensive Wastewater Discharge Standard. Moreover, there are drawbacks such as slow sedimentation of sludge, difficulty in dehydration, long processing cycles for high flow discharge, and inability to adapt to continuous treatment and discharge.

The adsorption method for fluoride removal mainly includes active alumina, clinoptilolite, active magnesium oxide, etc. In recent years, adsorbents with high fluoride adsorption capacity such as hydroxyapatite, zirconia, and cerium hydroxide have also been reported. Commonly used adsorbents such as clinoptilolite and active magnesium oxide have a smaller fluoride adsorption capacity of 0.06-2.0mg/g, resulting in poor treatment efficiency. The fluoride adsorption capacity of hydroxycalcium phosphate and active magnesium oxide reaches 3.5-10mg/g, but it is prone to loss during use. Rare earth element hydrated oxides and rare earth salts, represented by rare earth cerium and lanthanum, have strong affinity for anions such as fluorine and arsenate in water. Therefore, adsorbents mainly composed of rare earth elements have attracted attention both domestically and internationally due to their large adsorption capacity, low pollution, and convenient operation. The ion exchange and adsorption properties of rare earth elements as adsorbents are caused by the protonation reaction related to their surface hydroxyl groups. The mechanism of fluoride removal is the exchange of coordination water on metal ions with F - in solution. Most rare earth elements used as adsorbents load rare earth elements on fibrous materials with large surface areas, because fibrous adsorbents have a large specific surface area and strong mechanical strength, and the coordination ability of rare earth elements with F - is strong. Therefore, the combination makes rare earth metal oxides have a high adsorption capacity and strong adsorption selectivity for fluoride ions in water, and the fluoride adsorption capacity of the adsorbent reaches 30mg/g.

Rare earth adsorbents, whose protonation reaction only involves surface adsorption and are expensive, although they can be regenerated, their regeneration effect is average and the treatment cost is extremely high. There are also reports that adsorbents carrying cerium hydroxide on the surface of carriers such as aluminum or titanium have good adsorption effects on fluoride ions. However, regardless of the adsorption method, rare earth compounds, due to their unique fluorine affinity, can not only effectively remove excess fluoride in water, but also improve the surface structure of conventional filter media, increase the adsorption sites on the surface of filter media. They also have good effects on the removal of other impurities in water, such as heavy metal ions and some inorganic ions. Therefore, selective adsorption of fluoride ions cannot be carried out, and the adsorption efficiency of adsorbents is low. Especially when wastewater contains oil and organic pollutants, adsorbents will quickly saturate and almost cannot work normally. Therefore, using adsorbents for fluoride removal treatment is expensive, difficult to regenerate, and limited by other pollution factors in the wastewater during use, making it impossible to use it normally in production practice.

summary of the invention

In response to the shortcomings of the existing technology mentioned above, the present invention aims to provide a defluorination agent mainly composed of rare earth compounds, as well as a preparation method thereof, suitable for the removal of low concentration fluoride ion pollution factors in wastewater. Its characteristics are good and stable defluorination effect, low treatment cost, and recyclable generated rare earth fluoride.

To solve the problems existing in the prior art and achieve the purpose, the technical solution adopted by the present invention is: a wastewater defluorination agent, characterized in that the defluorination agent contains rare earth elements.

Furthermore, the rare earth elements are rare earth chloride or rare earth carbonate.

Furthermore, the defluorination agent formed by the rare earth chloride is an aqueous solution, with rare earth chloride accounting for 1-65% of the total mass of the defluorination agent, preferably 5-10%. The rare earth chloride is preferably lanthanum chloride, cerium chloride, praseodymium chloride or neodymium chloride.

Furthermore, the defluorination agent formed by the rare earth carbonate is in powder form, and the rare earth carbonate accounts for more than or equal to 80% and less than 100% of the total mass of the defluorination agent. The preferred rare earth carbonate is lanthanum carbonate, cerium carbonate, praseodymium carbonate, or neodymium carbonate.

Furthermore, the defluorination agent also contains polyacrylamide, with a mass of 0.1 ‰ -1 ‰ of the total mass of the defluorination agent.

Furthermore, the amount of polyacrylamide added is 0.1 ‰ -0.2 ‰ in a defluorination agent containing rare earth chloride, and 0.5 ‰ -1 ‰ in a defluorination agent containing rare earth carbonate.

The preparation method of a fluorine removal agent formed by rare earth chloride is as follows:

(1) Prepare rare earth chloride solution with a mass fraction of 1-65% and mix evenly;

(2) In the rare earth chloride solution described in step (1), a flocculant is added at a ratio of 0.1 ‰ to 0.2 ‰ of the total weight, mixed evenly, and a wastewater defluorination agent mainly composed of rare earth chloride is prepared.

The preparation method of a defluorination agent formed by rare earth carbonate is as follows:

Mix the proportion of rare earth carbonate with polyacrylamide and stir evenly.

A method for using a fluoride removal agent formed by rare earth chloride: the fluoride ion concentration in the influent of fluorine-containing wastewater is less than 50mg/L, the pH value is controlled at around neutral 7, and the fluoride ion to rare earth chloride fluoride removal agent is added according to the mass ratio of fluoride ions to rare earth chloride, stirred for 30 minutes, fully reacted, and left to settle for 60 minutes. After the formed precipitate is recovered, solid-liquid separation is carried out, and further used for rare earth smelting.

The method of using a defluorination agent formed by rare earth carbonate is as follows:

The fluoride ion concentration in fluorinated wastewater is less than 50mg/L, and the pH value is controlled at around 2.5. Rare earth carbonate defluorination agents are added according to the mass ratio of fluoride ions to rare earth carbonate, which is 0.22-0.29. Stir for 30 minutes, fully react, and settle for 60 minutes. The formed fluoride rare earth precipitate is recovered and solid-liquid separated for further use in rare earth smelting.

The principle of defluorination of the agent described in the present invention belongs to the ion precipitation method for removing fluoride ions. Fluoride ions combine with rare earth element ions to form rare earth fluoride precipitates, which are insoluble in water. Fluoride ions in water are removed through ion co precipitation, thus having good selectivity. The generated rare earth fluoride is recycled for rare earth smelting. The reaction equation is as follows:

F -+Re3+→ ReF3

The beneficial effects of the present invention are:

(1) The conventional addition of the fluorine removal agent of the present invention can make the fluoride ion concentration in the treated wastewater ≤ 5mg/L, lower than the first level discharge standard (below 10mg/L) specified in the Comprehensive Wastewater Discharge Standard (GB8978-2002), and lower than the special discharge limit (below 8 mg/L) specified in the Rare Earth Industry Pollutant Discharge Standard.

(2) The slightly excessive addition of the fluorine removal agent in the present invention can result in a fluoride ion concentration of ≤ 2mg/L in the treated wastewater, which is lower than the special emission limit for fluoride ions (below 2 mg/L) (below 10mg/L) specified in the "Emission Standards for Industrial Pollutants of Copper, Nickel, and Cobalt" (GB25467-2010).

(3) The defluorination agent of the present invention has selectivity in removing fluoride ions from wastewater and is not affected by other pollution factors such as oil, COD, SS, etc. in the wastewater. It can achieve fluoride ion removal under non strong alkaline conditions.

(4) The defluorination agent of the present invention achieves the purpose of removing fluoride ions through ion co precipitation. The rare earth element ions in the agent form fluorinated rare earth precipitates with fluoride ions, which are insoluble in water, nitric acid, hydrochloric acid, and sulfuric acid, and have very stable chemical properties; The generated precipitate of rare earth fluoride can be reused for rare earth smelting and re made into rare earth chloride as a raw material for fluoride removal agent production after solid-liquid separation. Rare earth elements are not lost during the fluoride removal process, greatly reducing the cost of wastewater treatment.

(5) The defluorination agent of the present invention can be applied to the production of polishing powder precursors when the purity of rare earth fluoride formed under certain wastewater quality conditions is high during the defluorination process of wastewater.

(6) This defluorination agent forms a precipitate of rare earth fluoride with fluoride ions in wastewater, which has finer particles and longer settling time. The present invention adds polyacrylamide as a flocculant to the defluorination agent to avoid the use of inorganic salt flocculants that combine with fluoride ions in wastewater to form precipitates, causing a large amount of impurities in the precipitate of rare earth fluoride, facilitating the recovery of rare earth fluoride, shortening the settling time of rare earth fluoride precipitates, improving the settling effect, and reducing the investment of defluorination settling equipment.

(7) Compared with existing technology, the defluorination agent of the present invention forms a recyclable fluoride rare earth precipitate through rare earth element ions and fluoride ions to remove fluoride ions. On the basis of ensuring that the fluoride ions in the effluent meet the standard, it can achieve the recovery and utilization of fluoride ions and rare earth elements in the defluorination agent, avoiding the problems of high usage cost and poor adsorbent regeneration effect caused by using rare earth element compounds as adsorbents.

Specific implementation methods

Example 1

The preparation method of the fluorine removal agent of the present invention is as follows:

Raw materials: lanthanum chloride solution (content 60%), polyacrylamide (granular, content 90%), pure water.

Preparation: (1) Dilute the 60% lanthanum chloride solution with water to 5% and mix well.

(2) In the 5% lanthanum chloride solution described in step (1), polyacrylamide is added in a ratio of 0.2 ‰, mixed evenly, and stirred for 1 hour to produce a wastewater defluorination agent mainly composed of lanthanum chloride.

Applied to the deep fluoride removal of a rare earth smelting wastewater, the influent fluoride ion concentration is 48mg/L, pH value is 7.14, and the discharge amount is 10m3/d. The addition of lanthanum chloride fluoride removal agent is 3.88kg/m3, the effluent fluoride ion concentration is 4.01mg/L, and the effluent pH value is 6.86. The recovery amount of lanthanum fluoride is 1.26kg/d, and the recovery rate is 83.4%.

Example 2

Raw materials: cerium chloride solution (content 65%), polyacrylamide (granular, content 92%), pure water.

Preparation: (1) Dilute a 65% cerium chloride solution with water to 10% and mix well.

(2) In the 10% cerium chloride solution described in step (1), polyacrylamide is added in a ratio of 0.1 ‰, mixed evenly, and stirred for 1 hour to produce a wastewater defluorination agent mainly composed of cerium chloride.

Applied to the deep removal of fluoride from a rare earth smelting wastewater, the influent fluoride ion concentration is 44mg/L, pH is 7.02, and the discharge amount is 12m3/d. The addition of cerium chloride fluoride removal agent is 1.73kg/m3, and the effluent fluoride ion concentration is 3.91mg/L, pH is 6.72. The recovery amount of cerium fluoride is 1.344kg/d, and the recovery rate is 83.6%.

Example 3

Raw materials: praseodymium chloride solution (content 56%), polyacrylamide (granular, content 88%), pure water.

Preparation: