SK13996A3 - Treatment method of waste water containing soluble phosphates by flocculation process - Google Patents

Abstract

This method uses the low dissolubility of the compounds of phosphates with calcareous ions where waste water is mixed with calcium hydroxide and calcium chloride. In the cleaned waste water first of all the pH is modified by calcium hydroxide in an aqueous suspension or in solution in a reactive mixture and then a molar ratio of the elements Ca<2+> and PO4<3-> is set by the solution of calcium chloride. After mixing the extracted precipitate is separated from the aqueous phase by sedimentation. Before terminating the mixing a polymeric organic flocculant is added to the reactive mixture, for example based on polyacrylamide.

Description

Process for the purification of waste water containing soluble phosphates by a precipitation process.

Technical field

The invention relates to a process for the purification of waste water heavily contaminated with phosphates in various ionic forms by a precipitation process.

BACKGROUND OF THE INVENTION

Waste waters from the chemical industry, containing soluble forms of phosphates, usually have a pH in the region of weakly acidic to weakly basic. In this pH range, phosphates are predominantly present in the form of dihydrogen phosphates and monohydrogen phosphates. In the purification of these waters, precipitation processes are generally used which utilize the low solubility of some phosphates, e.g. iron or calcium. In the case of the precipitation of iron phosphates, an excess of precipitant is required as a result of the inactivation of a portion of the reagent by hydrolysis, and the resulting product is more difficult to utilize for the presence of iron.

In the case of calcium phosphate precipitation, calcium hydroxide is usually used as a precipitation agent. However, calcium hydroxide is added by both components, and OH ”. When the required amount of ions of sparingly soluble calcium phosphate is added, the corresponding OH 'ions are in excess, therefore precipitation occurs in a strong alkaline region, in which the dissolution of calcium hydroxide is more difficult, which is shown negatively throughout the process. the precipitate formed is of the composition Ca ₅ (PO ₄ ) ₃ . (OH) with both Ca ²⁺ and Ca ²⁺ ions to eliminate the precipitation technology, predominantly hydroxylapatite, with a small proportion of calcium monohydrogen phosphate (CaHPO ₄ ) with a proportion of Ca: PO ₄ = 1.6: 1. After separation of the precipitate from purified water, it is necessary to adjust the pH by adding acid and undesirable before discharging into the effluent

Thus increasing the dissolved salt content. In addition, the dissolution of calcium hydroxide in the alkaline region is more difficult, which is reflected in the entire precipitation process.

SUMMARY OF THE INVENTION

It has now been found that for the purification of waste waters containing soluble phosphates by a precipitation process using low solubility of calcium phosphate compounds, the present invention is advantageous in that calcium hydroxide in water is added to the purified water. of a suspension or solution to adjust the pH in the reaction mixture within the range of 9.9 to 10.5 and a solution of calcium chloride in an amount such that the molar ratio of Ca: PO components in the resulting reaction mixture is 1.1 to 1.4 to 1. The reaction mixture is stirred. The precipitate formed is separated from the aqueous phase. Preferably, a solution of polymeric organic flocculant, for example a polyacrylamide-based substance, is added to the reaction mixture before the mixing is complete.

This method brings a number of advantages over the current state. The precipitation reaction proceeds immediately because it is not inhibited by the accompanying processes. The calcium ions entering the reaction are stoichiometric in the precipitate being formed, so there is no need for excess reagent. Adjusting the pH in purified water before discharge does not require large amounts of acid. The addition of the polymeric organic flocculant at the appropriate time then causes the formation of larger, well-settling particles.

DETAILED DESCRIPTION OF THE INVENTION

Example 1.

Waste water containing 6.4 mmol / l PO and 0.87 mmol / l

Ca ²⁺ at pH 4.35. To one liter of this water was added 8.2 mmol / l Ca (OH) ₂ in an aqueous suspension. The mixture reached a pH of 10.47. CaCl ₂ in a solution of 1.4 mmol / l is added to the mixture. After stirring, the mixture was allowed to settle for 30 minutes and then analyzed, the results of which are shown in the table below:

PH ca P0 ₄ Sludge volume 9.87 24 mg / l 7.8 mg / L 33%

Example 2.

Precipitation as in Example 1 except that one minute before the end of stirring, a polyacrylamide-type auxiliary flocculant is added in an amount of 2 mg / L. The resulting sludge volume after 30 min sedimentation was 21%.

Example 3.

To one liter of the waste water of Example 1 was added 7.3 nmol / L Ca (OH) ₂ in an aqueous suspension. The pH of the mixture was 10.05. CaCl ₂ in solution was added in an amount of 2.3 mmol / l. After stirring, the mixture was allowed to sediment for 30 minutes. The effluent had a pH of 9.78, contained 9.3 mg / L PO ₄ and a calubel volume of 36%.

Industrial Applicability

The invention has application in the purification of waste water from the chemical industry containing soluble forms of phosphates.

Claims (2)

PATENT CLAIMS A process for purifying waste water containing soluble phosphates by a precipitation process using low solubility of calcium ion phosphate compounds, characterized in that calcium hydroxide in an aqueous suspension or solution is added to the purified water to adjust the pH of the reaction mixture within the limits of 9.9 to 10.5 and a solution of calcium chloride in an amount such that the molar ratio of Ca: PO ₄ components was 1.1 to 1.4 to 1 in the resulting reaction mixture, the reaction mixture being stirred and the precipitate formed was separated from the aqueous phase. 2. Process for purifying waste water containing soluble phosphates by the precipitation process according to claim 1, characterized in that a solution of a polymeric organic flocculant, for example a polyacrylamide-based substance, is added before stirring is complete.