CS256030B1 - Process for preparing lime milk - Google Patents

Abstract

The purpose of the solution was to find a use for waste and salt water containing calcium sulfate. This goal is achieved by first quenching calcium oxide with technological, i.e. surface, utility or process water in the amount necessary to obtain solid calcium hydroxide, after which the solid calcium hydroxide is mixed in waste water containing calcium sulfate. The lime milk prepared in this way is suitable for neutralizing acidic waste water.

Description

The invention relates to a process for preparing lime milk.

An aqueous calcium hydroxide slurry, commonly called lime milk, is used industrially © especially as a cheap alkaline reagent suitable for neutralizing acidic media, for example at neutralization stations of chemical plants where acid wastewater is neutralized before being discharged into public streams. to be sufficiently reactive, the calcium hydroxide must be in suspension in the form of small non-agglomerated particles and the solid phase concentration in the suspension must not exceed a certain value, usually around 15% by weight.

Satisfactory lime milk is usually prepared by the continuous reaction of lump quicklime with surface, service or process water, hereinafter referred to as process water, which contains only a very small amount of dissolved by-products. Consumption of process water to prepare lime milk in a chemical plant producing strongly acid waste water is often so large that it adversely affects the entire water management of the company and at the same time disproportionately increases the volume of discharged water and thus the total amount of dissolved salts discharged into public streams ·

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An improvement in this state of the art is that the process water has extinguished lump lime to a very thick slurry, which is further diluted with waste saline water to a concentration suitable for transport and reaction properties. for the preparation of lime milk, the properties of the resulting lime milk being the same as if only process water was used ·

However, in large chemical plants, the use of technological water is too high *

A further reduction in process water consumption can be achieved by a process for preparing lime milk by reacting calcium oxide with water according to the present invention, characterized in that calcium oxide has been extinguished with process water in an amount necessary to obtain only solid calcium hydroxide, which is then mixed into waste water containing calcium sulphate ·

In addition to the maximum saving of process water, the method according to the invention achieves an absolute reduction in the amount of soluble salts discharged into the public streams.

The method according to the invention is based on our new experimental finding that a suspension of solid calcium hydroxide in waste water containing dissolved calcium sulfate does not differ in reactivity and technological properties from lime milk prepared by traditional slaking of lump quick lime with process water.

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The lump quick lime is first hydrated with process water in the form of a liquid or steam, for example in a screw or drum apparatus, where a fine calcium hydroxide powder is formed. The resulting dry calcium hydroxide is then stirred in saline-containing waste water containing calcium sulfate to the desired concentration. The suspension thus prepared can be stored in conventional containers without excessive sedimentation, and also the reaction of the suspension with acid or acidic effluents proceeds sufficiently quickly and completely.

Example

The lump burnt lime was fed to the screw extinguisher together with process water at a weight ratio of 1: 0.65. The resulting calcium hydroxide powder was then mixed in a waste water containing 2% w / w calcium sulfate to a 15% w / w suspension. '. The suspension did not cause any problems. The technological and chemical properties of the lime milk suspension thus prepared were identical to those of lime milk prepared using process water only.

Claims (1)

Process for preparing lime milk by reacting calcium oxide with water, characterized in that the calcium oxide has been extinguished with process water in an amount necessary to obtain only solid calcium hydroxide, which is then mixed in the waste water containing calcium sulfate.