RU2411194C2 - Method of reducing content of calcium ions in waste water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in mineral processing using a floatation method, where content of calcium in recycled water is limited. Calcium ions are removed from waste water through successive addition of a carbonate of an alkali metal and an alkali with subsequent separation of the residue which is difficult to dissolve. The alkali metal carbonate used is calcined soda. After adding an alkali to pH 11.0-11.5, an anionic surfactant - crude tall oil soap - is added to form floccule, and a coagulant - iron sulphate, is added. To intensify formation of floccule and increasing the rate of precipitation, concentration of anionic surfactants is 20-70 mg/l. To remove the formed floccule through floatation, concentration of anionic surfactants is 50-100 mg/l.

EFFECT: invention ensures content of calcium in purified water of up to 1 mg/l and rate of precipitation higher than 0,16 mm/s.

3 cl, 1 tbl, 6 ex

Description

The invention relates to the beneficiation of minerals by flotation using recycled water and can be used in other industries where the calcium content is limited.

As you know, an excess of calcium ions (more than 20 mg / l) in the circulating water leads to a violation of the selectivity of the flotation process. Given the amount of circulating water consumed, preparing circulating water, reducing the content of calcium ions, is uneconomical. Therefore, it is advisable to prepare the discharged water of individual workshops, in the wastewater of which contains the largest amount of calcium ions. Such workshops include thermal power plants, where the removed pulp of gas ash removal (GZU) contains up to 370 mg / l of calcium. This pulp, entering the tailings, gradually increases the content of these ions.

Various methods are known for adjusting the Ca ²⁺ content in water.

So, there is a known method of removing calcium ions by the ion-exchange method (Water treatment at thermal power plants. / Baulina A.I., Gurvich S.M., Kvetkovsky V.M. et al. // M.-L .: "Energy". - 1966. - p.209-242). For the preparation of recycled water, this method is not applicable due to the content of the solid phase in this water, the complexity of the hardware design with the regeneration of filter fillers, and for economic reasons.

There is also known a method of removing calcium ions by the soda-soda method, where water is treated with hydrated lime and soda. This method is used to remove stiffness up to 0.35-1 mEq / l (L.A. Kulsky. “Theoretical foundations and technology of water conditioning.” / Kiev: “Naukova Dumka” - 1971, - p.372; V.A. Klyachko, I.E. Apeltsin, "Purification of Natural Waters." / Moscow: Publishing Books on Construction. - 1971, - p. 343-350).

In addition to the hardness limit indicated above, it is necessary to monitor the dosage of lime, its excess leads to irrational overuse of soda. To reduce the stiffness in this way below the specified limits, it is recommended to heat the water, which is not economical with large volumes of purified water.

. Однако суспензия образующейся труднорастворимой соли СаСО₃ может находиться во взвешенном состоянии несколько часов, что затрудняет использование этого способа. Следует отметить также необходимость обозначения четких параметров процесса, в первую очередь, значений рН, т.к. существует зависимость от этих значений перехода бикарбонатной формы

в карбонатную

, что определяет степень умягчения воды.The closest solution is to soften the water with the introduction of alkali and alkali metal carbonate, followed by neutralization with food acid, such as phosphoric acid. Water purification to accelerate the process is carried out at elevated temperatures, softened water is brought to a boil and boiled for 3 minutes. Such water treatment involves additional costs for heating water (US Pat. RF No. 2091334), which is not acceptable for industrial use with large volumes of water. It is based on adjusting the pH of the medium and introducing for binding Ca ²⁺ anions

. However, the suspension of the resulting sparingly soluble CaCO ₃ salt may remain in suspension for several hours, which makes it difficult to use this method. It should also be noted the need to designate clear process parameters, primarily pH values, because there is a dependence on these transition values of the bicarbonate form

to carbonate

that determines the degree of water softening.

The aim of the present invention is to increase the efficiency of wastewater treatment from calcium ions and to intensify the removal of the resulting suspension of insoluble salt.

This goal is achieved by the introduction of an alkali metal carbonate at a pH above 11.0, anionic surfactants, such as crude tall oil soap (MCMT), inorganic coagulant, iron sulfate, and a second increase in pH values to values above 11.0. When all the above actions are performed, the content of calcium ions in the prepared water is below 10 mg / l (0.2 mEq / l), which meets the requirements of the flotation process at the Apatit concentrators. The intensification of the removal of the suspension of the formed sparingly soluble CaCO ₃ salt is associated with the need to achieve the maximum possible clarification rates, which in turn is associated with the area of the settlers. After purification, water enters the tailing dump, where the pH values are equalized due to the presence of alkaline minerals in the factory tails and the presence of slightly acidic plums obtained after concentration of the concentrates.

The essence of the proposed method consists in the formation of a sparingly soluble CaCO ₃ salt after the addition of an alkali metal carbonate at pH values above 11.0, for which alkali is supplied. An increase in pH converts bicarbonate ions to carbonate, and pH values equal to or higher than 11.0 provide such a transition by more than 80%. To form coagulation nuclei, small amounts of MCTM are added to the water after soda, which forms fatty acid calcium salts, the solubility product of which is 10 ^-12.4 , for comparison, the solubility product (Pr) of CaCO ₃ is 4.8 · 10 ^-9 (M.A. Eigelés. “Fundamentals flotation of non-sulfide minerals. "- M .: Nedra. - 1964, - p.132). To accelerate the coagulation process, an inorganic coagulant is then introduced, the introduction of which reduces the pH of the prepared water to values below 10.5-10.6, which reduces the degree of conversion of bicarbonates to carbonate ions to 60% or less and, accordingly, increases the content of calcium ions in the purified water. In order to maintain the required content of carbonate ions, the pH of the purified water is raised to the initial values (pH 11.2). With this approach, the rate of clarification of recycled water increases to 0.178 mm / s and higher, which ensures the operation of 3 thickeners with a diameter of 30 m, available at the factory with a feed water capacity of 1250 m ³ / h.

The second way to remove the resulting flocs from the purified water is flotation. As shown above, the addition of anionic surfactants accelerates the process of flocculation, because The calcium oleate and iron (II) oleate are equal to 10 ^-12.4 . For flotation floccule removal, the concentration of MCMT will be 50-100 mg / L, which is higher than that required for intensification of flocculation. In principle, based on Pr salts of fatty acids, it is possible to purify water from multivalent cations using surfactants, but this is possible when they are used to remove valuable metal ions from water, because in other cases, this does not justify itself economically.

The proposed method for the removal of calcium ions from water can be explained by the following examples.

в виде карбоната щелочного металла, затем довели до значений рН 11.2. После чего ввели железный купорос до концентрации 70 мг/л, рН очищаемой воды снизился до 10.8. Скорость осаждения флокул составила 0.1 мм/сек, а содержание ионов кальция - 9.72 мг/л, содержание «взвешенных» - 114 мг/л.Example 1. In the water containing 79 mg / l of calcium, was introduced 120 mg / l

in the form of an alkali metal carbonate, then adjusted to pH 11.2. After that, iron sulfate was introduced to a concentration of 70 mg / l, the pH of the purified water decreased to 10.8. The floccule deposition rate was 0.1 mm / s, and the content of calcium ions was 9.72 mg / l, the content of “suspended” was 114 mg / l.

Example 2. In the water containing calcium ions, the components of Example 1 were introduced, but the consumption of iron sulfate was increased to 150 mg / L, the pH after adding soda and alkali was 11.21, and after adding iron sulfate to increase the deposition rate of floccules - 10.28. The calcium content in purified water was 32.52 mg / l, and the deposition rate of flocs was 0.15 mm / s, and the content of suspended particles was 92 mg / l.

Example 3. The reagents of Example 1 were introduced into the test water, but before iron sulfate, the concentration of which was 70 mg / L, MCM was added to a concentration of 50 mg / L, the pH of the water was 10.87. The calcium content in purified water was 15.05 mg / l, and the deposition rate of flocs was 0.12 mm / s, the content of "suspended" was 150 mg / l.

Example 4. In the test water was introduced the reagents of example 3, but the concentration of iron sulfate was increased to 150 mg / l, the pH of the water was 10.17. The concentration of calcium ions in purified water was equal to 30.45 mg / l, and the deposition rate was 0.16 mm / s, the content of "suspended" was 87 mg / l.

Example 5. The reagents of Example 4 were introduced into the test water; after entering all the reagents, alkali was added to a pH value of 11.2. The calcium content in the purified water was 9.62 mg / l, and the floccule sedimentation rate was 0.172 mm / s.

In examples 1, 2, the time to reach the coagulation threshold was 20 seconds, and in examples 3, 4, 5-5 seconds.

Example 6. The test reagents were introduced into the test water according to example 5, the difference was that MCMT was introduced after iron sulfate. The calcium content in purified water was 25.6 mg / l, and the deposition rate of flocs was 0.168 mm / s, and the content of "suspended" was 82 mg / l.

All results of these experiments and subsequent are given in the table.

с учетом перехода бикарбонатных ионов в карбонатные для образования труднорастворимой соли СаСО₃. Вывод этой соли из очищаемой воды может осуществляться осаждением при вводе железного купороса с корректировкой значений рН до значений, равных 11.2, и интенсификацией флокулообразования вводом МСТМ. Ввод МСТМ осуществляется перед подачей железного купороса. Снижение порога коагуляции в системе характеризует интенсификацию флокулообразования.Thus, the proposed method for purification of wastewater from calcium ions allows to reduce their content to values of 10 mg / l and lower, while observing stoichiometric ratios of Ca ²⁺ and

taking into account the transition of bicarbonate ions into carbonate ions to form a sparingly soluble CaCO ₃ salt. The withdrawal of this salt from purified water can be carried out by precipitation during the introduction of iron sulfate with the adjustment of pH values to values equal to 11.2, and the intensification of flocculation by the introduction of MCMT. The input of the MSTM is carried out before the supply of iron sulfate. A decrease in the coagulation threshold in the system characterizes the intensification of flocculation.

To remove floccules formed by flotation, the concentration of anionic surfactants is in the range of 50-100 mg / L. Below these concentrations, the content of suspended ones increases, and above it is impractical, because at 100 mg / l, the content of "suspended" in purified water is 82 mg / l.

Claims (3)

1. The method of purification of wastewater from calcium ions, including the introduction of an alkali metal carbonate and alkali, followed by separation of an insoluble precipitate, characterized in that soda ash is used as an alkali metal carbonate, and after the introduction of alkali to pH 11.0-11.5, anionic surfactant - soap of crude tall oil for the formation of flocs, and then the coagulant - iron sulfate. 2. The method according to claim 1, characterized in that for the intensification of flocculation and increase the deposition rate, the concentration of anionic surfactants is 20-70 mg / L. 3. The method according to claim 1, characterized in that to remove the flocs formed by flotation, the concentration of anionic surfactants is 50-100 mg / L.