Universum: технические науки

 
Keywords: 
adsorption,
 
bioadsorbents, heavy metal ions, wastewater treatment, fertilizers, modification. 
Ключевые слова: 
адсорбция, биоадсорбенты, ионы тяжелых металлов, очистка сточных вод, удобрения, 
модификация. 
________________________________________________________________________________________________ 
INTRODUCTION 
Among the main pollutants that have a negative im-
pact on the state of natural water bodies are heavy metal 
ions coming with wastewater from oil refining, metal-
lurgical, galvanic, tanning and other enterprises.
The production of mineral fertilizers is one of the 
most intensively developing industries in the Republic 
of Uzbekistan. At the same time, an increase in the pro-
duction of various types of fertilizers, an expansion of their 
range, an increase in the quality and competitiveness 
of products is associated with an increase in emissions 
of various types of pollutants into the environment in the 
form of gas and dust emissions, waste water and solid 
waste. The production of mineral fertilizers is associated 
with the formation of large volumes of wastewater con-
taining nitrogen compounds, heavy metals, oil products, 
etc. 
Despite the fact that at present at the enterprises for 
the production of mineral fertilizers there are treatment 
facilities that include mechanical, physicochemical and 
biological treatment methods, the degree of wastewater 
treatment does not always meet the requirements for the 
quality of treated water. This leads to the discharge of 
incompletely treated wastewater into natural reservoirs 
and disruption of the biological balance of the reservoir, 
the death of flora and fauna. 
At present, reagent methods are most often used to 
remove heavy metal ions from wastewater, in which 
metal ions are converted into an insoluble form with 
subsequent sedimentation of sludge. At the same time, 
these methods are uneconomical and have a number of 
disadvantages, such as incomplete removal of metals, 
high consumption of reagents and energy, as well as the 
formation of toxic sludge or other waste that requires 
disposal or processing [1, p. 373]. 
The purpose of this work was to study the process 
of purification of wastewater generated in the production 
of mineral fertilizers at "Maxam-Chirchik" enterprise. 
The technological scheme of wastewater treatment from 
Cu
2+
and Ni
2 +
ions by the reagent method includes av-
eraging the incoming effluents, treating them with rea-
gents to convert them into an insoluble form, settling the 
formed particles in a sump and dewatering sludge. 
Extraction of copper from wastewater is carried 
out by precipitation of copper with a CuS-solution 
of sodium sulphide with a mass fraction of 5-10%. 
The extraction of nickel is carried out by precipitation 
with a solution of lime milk with a mass fraction of 5% 
in the form of nickel hydroxide, as well as by galvanic 
coagulation in the form of nickel. Wastewater contains 
copper sulphide CuS; nickel hydroxide Ni(OH
2
); iron hy-
droxide Fe(OH
2
); chromium hydroxide Cr(OH
2
); zinc 
hydroxide Zn(OH
2
). During the sedimentation process, 
a large amount of sludge is formed, which has poor sed-
imentation properties and is difficult to separate from 
water. The sedimentation process takes place in a sump 
for 5 hours [2, p. 312 ].
After reagent treatment, wastewater is fed to biolog-
ical treatment facilities to remove nitrogen compounds 
by nitro-denitrification and then to clean them from or-
ganic compounds into aerotanks, after which they are 
discharged into the Chirchik river. However, recently, 
due to the tightening of environmental legislation and the 
introduction of strict standards for maximum permissible 
discharges into water bodies, reagent methods do not 
provide the required quality of wastewater treatment. 
In addition, metal ions remaining in the water, even in 
small amounts, can have a detrimental effect on acti-
vated sludge microorganisms during biological treatment, 
which also reduces the degree of water purification.
In this situation, from an economic point of view, 
many industrial enterprises do not have the opportunity 
to reconstruct the existing treatment facilities and switch 
to more efficient technologies for treating wastewater 
from heavy metal ions capable of providing complete 
purification. In this regard, to solve this problem, it 
seems to be effective to use additional wastewater treat-
ment. Post-treatment means methods and methods that 
complement reagent cleaning methods. The most effec-
tive and cheapest method of post-treatment is the ad-
sorption method of purification using natural and syn-
thetic sorbents. 
Recent studies show that one of the effective ad-
sorption materials that can be used instead of expensive 
synthetic adsorbents are bio-adsorbents obtained from 
agricultural waste [3, p.2350].
In this work, studies were carried out on the use of 
bioadsorbents obtained on the basis of rice husks by 
modifying it with a 1% solution of alkali NaOH and 
caustic soda Na
2
CO
3
for additional purification of 
wastewater from the production of mineral fertilizers 
from heavy metal ions. 
To obtain adsorbents, rice husks were washed with 
water and dried at 105°C. Next, a 10-gram sample was 
poured with 1% NaOH alkali solution and kept for 

---

№ 10 (91)
октябрь, 2021 г. 
80 
24 hours with constant shaking. After that, the water was 
filtered off, washed with water until neutral, and dried to 
constant weight. Samples treated with soda Na
2
CO
3
were prepared in the same way. 
The obtained adsorbents were used for additional 
purification of waste water from copper and nickel ions 
formed at the “Maxam-Chirchik” enterprise. The studies 
were carried out with model solutions that completely 
imitate the effluents of this production. 
The study of the adsorption properties of the ob-
tained adsorbents was carried out on model solutions 
containing copper and nickel ions under static condi-
tions. To determine the adsorption capacity of the ob-
tained adsorbents, waste water solutions with a concen-
tration of 5 to 200 mg/L were prepared by diluting the 
initial solution. In flasks with a volume of 250 ml, 100 
ml of a solution of various concentrations were poured 
and 1 g of the modified adsorbent was added. The flasks 
were kept for 24 hours with constant shaking on the 
plug. After that, the solutions were poured off, filtered, 
and the content of metal ions was determined by the 
atomic absorption method. 
The amount of adsorption was determined from the 
decrease in the concentration of metal ions in the solu-
tion by the formula: 
(
)
%
100
m
С
C
V
A
final
initial
−
=
V – volume of the test solution, ml; 
C
initial
и С
final
– initial and final concentration of met-
als in water, mg / l; 
m – mass of adsorbent, g. 
The fig. 1 shows the curves of the dependence of the 
adsorption value of copper and nickel ions on the equi-
librium concentration of the investigated solutions.