CS257658B1 - Method of removing heavy metals from wastewater - Google Patents

Abstract

The removal of heavy metals, especially from wastewater, is addressed by the coagulation process. It is carried out by two-stage mixing, in the first stage a neutralizing agent is dosed into the solution while the solution is homogenized by mixing at a gradient value of 0 « 100 to 1000 s-1 for 2 to 20 minutes, and in the second stage the solution is mixed for 20 to 50 minutes, at a G in the range of 80,000 to 300,000, after which the sludge is separated.

Description

The present invention relates to a method for removing heavy metals from waste water.

Most wastewater treatment stations use to remove heavy metals from solutions by forming insoluble hydroxides or hydrated oxides in the alkaline pH range. Tin actually forms a colloidal dispersion. Their ability to coagulate must be exploited. The neutralization of wastewater produces colloidal particles of heavy metal hydroxides. The core of the colloidal particle is formed by the microparticles of hydroxides, on their surface they form ions forming the inner ionic layer · It is ionic adsorption, which follows the Paneth-Pajans rule · This inner ionic layer imparts to the colloidal nucleus an electric charge · The outer ion layer is then bound by electrostatic forces, creating an electric bilayer · Part of the bilayer adheres to the particle as the particles move through the environment and part moves with the liquid, each having the same charge but opposite signs. called the zeta potential. Its value is usually in the range of $ 0 to 100 mV. Below 30 mV, slow coagulation of particles occurs and zeta potential values around zero occur, rapid coagulation occurs · Relative stability of colloidal dispersions is caused by a number of factors:

- the electrical charge carried by the particles is played by simultaneously charged particles in adhesion,

- lyosphere - ie · a layer of dispersion medium attached to the surface of the adsclpel particles forms a protective coating around the particle

- protective colloid - the adsorption of which forms a protective coating on the surface

If the particles are to be coagulated, the stability factor must be violated. The coagulation process itself has two parts. In the first phase, particle aggregation occurs based on Brown's motion and is called perikinetic coagulation.

Ortho-kinetic coagulation occurs after particle size increases as sedimentation begins to occur. · At this stage, particle growth is accelerated by colliding particles from different sedimentation rates (vertical ortho-kinetic coagulation). The velocity gradient between two horizontal layers is called the velocity gradient. The effect of the velocity gradient on the number of particle encounters was then mathematically formulated by Smoluehovski. Perlkinetic coagulation is shortened by increased turbulence of the agitated mixture · For the formation of large flakes, ie · aging of the suspension, however, the turbulence must not exceed certain discrete values, since the already formed large flakes are re-broken ·

A number of mathematical formulas were derived to determine the most suitable gradient supplied in tulle flocculation tanks. One of the basic relationships is the formula for calculating the speed gradient and power:

t · we χ is the viscosity

Py yo work per unit of time in unit of volume O is the speed gradient ·

The gradient value expresses the mixing efficiency but does not determine its duration. This includes the so-called Camp's Ca number:

Ca · G · t where t is the mixing time (flocculation) ·

However, in all current purification stations, the entire process is conducted only as a neutralization process, regardless of the need to ripen the suspension. This leads to a significant discharge of heavy metals into the outflow ·

The process according to the invention is based on the fact that the coagulation process is carried out under a two-stage agitation process, the

- 3 water is added as a neutralizing agent sodium hydroxide, to adjust the waste water to a pH of 8 to 11, and at the same time to homogenize the solution by stirring at values of 0 * 100 to 1000 s for 2 to 20 minutes, and The solution is stirred mechanically at a gradient of 6 to 80,000 to 300,000 for 20 to 50 minutes, after which the sludge is separated.

The higher effect of the invention is manifested in that it substantially reduces the discharge of heavy metals from the streams to the effluent, in particular in the treatment of waste water, which also allows the removal of sludge microparticles from these waters.

The practice of the invention consists in that in the first stage, the waste water is dosed as a neutralizing agent with a sodium, potassium or calcium hydroxide solution under rapid stirring to achieve complete homogenization of the entire mixture · Mixing can be mechanical or ejector dosing In the second stage of the treatment, the sludge matures - flocculation - when the sludge microparticles are also wrapped in the flakes. At this stage the reaction mixture must be mechanically stirred more slowly, preferably with wooden paddles.

In case of using polyflocculants it is necessary to perform their dosing at the end of rapid mixing · After the slow mixing is finished, the sedimentation mixture must not be pumped again so as not to break the formed flocs · Only by gravity is allowed ·

The sedimentation time varies according to the nature of the sludge formed. Example 1

The waste water contained Ni -54 mg.1 " ¹ , Cu - 27.3 mg ·! * ¹ ,

Cr - 50 mg.l ^-1 at pH 3.7 and was adjusted to pH 8.3 by addition of 30% NaOH solution with rapid stirring Ca * 120,000. At the end of rapid stirring, Pre table 2934 polyflocculant was dosed at 2 mg.l. ” ¹ . Time t 300 s · Slow agitation followed by time t 1500 s, Ca 110 000 and sedimentation for 1.5 hours ·

In the samples taken after the water treatment, the following concentrations were found: Ni - 0,07 mg ·! “ ¹ , Cr * ¹³ “ - 0,03 mg.l “ ¹ , Cu - 0,05 mg ^ l“ ¹ · Equally treated The waste water, which was omitted from the slow mixing phase, showed the following residual concentrations: Ni - 0.27 mg ·! "*, _Cr XII ~ 005 mg.l" ¹ , Cu - 0.1 mg ·! " ¹ ·

Example 2

The waste water contained Cu - 200 mg.l ^-1 , for ~ 48 mg.l ^-1 ,

P * - 3.5. For rapid agitation, Ca * 150,000, -1 * 400 s, and for slow agitation, Ca 200 200,000, t 1800 1800 s. The pH was adjusted to 8.7 by KaOH dosing. After a two-hour sedimentation period, nalosones of residual concentration (bos using polyflocculant) were Cu * 0.1 mg.l, Zn - 0.1 mg.l, pH 8.5. With the omission of the slow mixing phase, the following residual concentrations were found to be non-Cu: 0.28 mg.l ^-1 t Zn - 0.32 mg.l ^-1 . Example 3

The waste water contained Ni - 30 mg.l ** ¹ , Zn - ¢ 2 mg.l “ ¹ ,

Mo - 20 mg.l “ ¹ . The pH value was adjusted to 9.1 with lime milk with rapid stirring over 600 s, Ca · 200 000, at the end of which a polyacrylamide-based polyflocculant was dosed

2.5 mg.l ** ¹ . Slow agitation lasted 1800 a · Ca 140 000. Samples were analyzed after two hours of sedimentation, the residual concentration was Mi - 0.12 mg.l ^-1 , Zn -0.1 mg.l ^-1 , Pe - 0.03 mg. l “ ¹ . The same treated bass sample using slow mixing contained a higher residual concentration: Mi - 0.21 mg.l ^-1 ,

At - 0.2 mg.l * ¹ and Po - 0.04 mg.l ^-1 .

Claims (1)

Method of removing heavy metals from wastewater by their noutrallsation and formation of non-permeable hydroxides or hydrated oxides in alkaline pH range and subsequent coagulation! characterized in that a two-stage mixing is carried out, in which, in the first stage, an alkali metal hydroxide or alkali metal hydroxide, for example, sodium hydroxide, is added to the waste water as a neutralizing agent to treat the waste water to pH 8-11; at a gradient of G · 100 to 1000 s ^-1 for 2 to 20 minutes »and in the second stage the rostok is mechanically stirred at a G gradient of 80,000 to 300,000 for 20 to 0 minutes» after which the sludge is separated.