CS261610B1 - Process for preparing lime milk - Google Patents

Abstract

The solution concerns a method of utilizing saline wastewater for the preparation of milk of lime. This objective is achieved by first reacting quicklime with process water to prepare a calcium hydroxide suspension with a concentration of 20 to 50% by weight, after which this thick suspension is diluted to the required concentration with water containing dissolved electrolytes, such as calcium sulfate.

Description

The invention relates to a process for preparing lime milk.

An aqueous suspension of calcium hydroxide, commonly called lime milk, is very often used in the industry as an inexpensive alkaline agent, particularly suitable for neutralizing acidic media. A typical example of the use of lime milk in industry may be chemical plant neutralization stations where acid wastewater is neutralized with a calcium hydroxide slurry prior to discharge into public streams. Lime milk suitable for this use must meet a number of requirements, the most important of which are: sufficiently high reactivity to allow the neutralization reaction to proceed quickly and completely in terms of the use of calcium hydroxide, the calcium hydroxide in the suspension must be present as small particles mostly unreacted, leading to high calcium hydroxide consumption and causing high residual alkalinity of the solid product of the neutralization reaction, in the calcium hydroxide slurry the particles must not tend to form large primary particle clusters and the solid phase content of the slurry must not exceed a certain value otherwise its transport and reaction properties.

Lime milk that meets the above requirements is commonly prepared by continuously guided reaction of lump quicklime with process water containing no large amount of soluble electrolytes. Since lime milk is prepared at a concentration of about 12% by weight of calcium hydroxide, the consumption of process water, for example, at the neutralization station of a chemical plant producing acid waste, is so high that it adversely affects the water management of the company. Likewise, the volumes of discharged water and their total salinity, which goes into public watercourses, have an adverse impact on both the company's management and the environment.

Therefore, ways have been sought to replace the process water necessary for quenching lump quicklime with waste water from the plant, which generally contains dissolved electrolytes, such as calcium sulfate. All experiments of this kind have resulted in a decrease in the reactivity of lime milk, a reduction in the final reaction stage in neutralization, and in the formation of suspensions forming rapidly settling clusters of particles, even when only part of the technological process has been replaced.

waste water (dilution). In addition, the proportions of large and heavy particles often formed which were completely unreactive and always settled very quickly. In light of these facts, in the preparation of lime milk by slaking quicklime, it is said that clean technological water cannot be replaced by any type of wastewater, even if it is partially salinized.

The above-mentioned operating experience has been overcome by the process of preparing lime milk according to the invention, which consists in first preparing a calcium hydroxide slurry at a concentration of 20 to 50% by weight and then diluting the thick slurry to the required concentration. water containing dissolved electrolytes such as calcium sulfate.

In other words, a very dense calcium hydroxide slurry is first prepared by slaking lime with non-saline process water, and the slurry thus prepared is diluted with waste water containing dissolved electrolytes, such as calcium sulfate, to a lower technological concentration, e.g. 10% by weight of Ca (OH) 2. The lime milk obtained has neither reduced reactivity nor impaired sedimentation properties compared to the case where only pure process water is used and, moreover, the amount of saline water discharged into public streams is reduced.

The procedure for preparing lime milk using water saturated with calcium sulfate is apparent from the following example.

Example

The lump quicklime is fed into a fire extinguisher cylinder with a quantity of pure process water to produce a calcium hydroxide slurry having a concentration of approximately 25% by weight of the solid phase. Prior to exiting the extinguishing cylinder, the slurry is diluted with calcium sulfate waste water to a concentration of 12% by weight of the solid phase. The suspension thus prepared is then passed through a sorter into containers from which it is withdrawn for the need of a neutralization station. The technological and chemical properties of the suspension are identical to the calcium hydroxide suspension prepared only using pure process water free of dissolved salts.

Claims (1)

Subject Process for preparing lime milk, characterized in that by first reacting quicklime with process water, a calcium hydroxide suspension having a concentration of yNALEZ is prepared. 20 to 50% by weight, and then the thick suspension is diluted to the desired concentration with water containing dissolved electrolytes, such as calcium sulfate.