Yulök Revista de Innovación Académica, ISSN 2215-5147, Vol. 7, N.º 2

Junio-Diciembre 2023, pp. 64-74

Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

Characterization of sludge from

industries for possible recovery in Arts

Karina Rodríguez Mora

Universidad de Costa Rica, Instituto de Investigaciones en Ingeniería. Unidad de Recursos Forestales, San José, Costa Rica

karina.rodriguezmora@ucr.ac.cr

https://orcid.org/0000-0001-9660-4623

Abstract

Sludge from oxidation ponds from different industries was evaluated to study its composition through a chemical characteri-

zation and to determine a possible route for its recovery. For the characterization of the sludge, gravimetry for SiO2 content,

infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, X-ray energy dispersion spectrometry (EDS), and X-ray

fluorescence (XRF) were used. It was determined that the paint industry sludges have a higher SiO2 content with 17.2 ± 0.2

% by mass and different phases present in the sludges such as albite, quartz, and rutile were identified, as well as metals of

interest in pigments such as iron, chrome, and zinc. The previous demonstrates that even though the matrix is highly complex;

there are routes for the use of this residue.

Keywords: Art, materials, pigments, sludge, wastewater.

Resumen

Se evaluaron lodos de lagunas de oxidación, provenientes de diferentes industrias con la finalidad de estudiar su composición

mediante una caracterización química, así como determinar una posible ruta para su valorización. Para la caracterización de

los lodos se utilizó gravimetría para el contenido de SiO2, espectroscopía infrarroja, difracción de rayos X, análisis termogra-

vimétrico, espectrometría de dispersión de energía de rayos X (EDS) y fluorescencia de rayos X (XRF). Se determinó que los

lodos provenientes de la industria de pinturas poseen un mayor contenido de SiO2 con un 17,2±0,2 % en masa y se identifica-

ron diferentes fases presentes en el lodo como albita, cuarzo y rutilo, además de metales de interés en pigmentos como hierro,

cromo y zinc. Mostrando que a pesar de que la matriz es altamente compleja existen rutas de aprovechamiento de este residuo.

Palabras clave: Arte, agua residual, lodos, materiales, pigmentos.

Caracterización de lodos de industrias para un

posible aprovechamiento en artes

Referencia/ reference:

Rodríguez, K., Jirón, E. y Hernández, V. (2023). Characterization of sludge from industries for possible recovery in Arts.

Yulök Revista de Innovación Académica, Vol.7 (2), 64-74. https://doi.org/10.47633/yulk.v7i2.592

Recibido: 8 de marzo 2023 Aceptado: 28 de mayo 2023

Eddy Jirón García

Universidad de Costa Rica, Escuela de Ingeniería Química, Sede del Caribe, Limón, Costa Rica

eddy.jiron@ucr.ac.cr

https://orcid.org/0000-0002-7524-9033

Verónica Hernández Solís

Universidad de Costa Rica, Escuela de Ingeniería Química, Sede Rodrigo Facio, San José, Costa Rica

veronica.hernandez@ucr.ac.cr

https://orcid.org/0009-0005-9019-5319

Yulök Revista de Innovación Académica, ISSN 2215-5147, Vol. 7, N.º 2

Junio-Diciembre 2023, pp. 64-74

Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

Introduction

The Facultad de Bellas Artes de la Universidad de Cos-

ta Rica (Faculty of Fine Arts of the University of Costa

Rica) seeks to promote art, that is, the ability to express

beauty through painting, sculpture, and music (Real Aca-

demia Española, 2021). This entity together with the Es-

cuela de Bellas Artes (School of Fine Arts) has a genuine

interest in contributing to professional training, and the

generation and dissemination of knowledge in the area of

the arts since 1897 to benefit the development of social

protection and recognition of the diversity of cultural he-

ritage from their undergraduate and postgraduate courses

(Facultad de Artes, 2023). All this while raising aware-

ness about environmental responsibility and promoting a

policy for the use and reuse of waste.

The waste that will be used and reused as raw material in

art is the sludge that is generated in the wastewater treat-

ment plants (PTAR) as a product of the conditioning of

the water for its discharge (Zhu et al., 2020). The oxida-

tion ponds in WWTPs are the most used option for water

treatment (Metcalf et al., 1991). At the bottom of these

lagoons, the large amount of sludge that is generated must

be extracted regularly so it can be used in various appli-

cations.

Sludge is divided into primary sludge and secondary

sludge. Primary sludges usually contain a lot of orga-

nic matter and high activity of microorganisms (Kwar-

ciak-Kozłowska, 2019), while secondary sludges are

found in oxidation ponds with little organic load and high

contents of water, silicates, clays, carbonates, and metals

(Canziani & Spinosa, 2019). The latter is of great interest

because of their chemical composition of some pigments,

glass, ceramics, and enamels. (Esteves et al., 2010).

In recent years, different initiatives for the use of sludge

have been launched for energy use (G. Yang et al., 2015;

Yi et al., 2014); as an addition to soils to improve their

quality (Kwarciak-Kozłowska, 2019; Passuello et al.,

2012); as an incorporation into construction materials as

reinforcement, (Camareno et al., 2006) and even to pro-

duce higher value materials such as zeolites (Carranza &

Montero-Villalobos, 2016).

However, it is established that the applicability of the slu-

dge from the industries in Fine Arts, from now is only

called Arts; can be in painting and sculpture. The possi-

bility of its use in music is excluded. Secondary sludge is

the most viable for this purpose. In this sense, there is the

use of mud in the work of Guy Riefler when extracting

pigments from the mud of the rivers of the coal mines in

southeastern Ohio, United States. With it, John Sabrow

gave color to his artistic works (Balmer, 2015). Likewise,

obtaining ceramic pigments spinel of Ni(Cr

, Fe

)

by Carneiro et al., (2018) using red mud, the use of ye-

llow waste sludge with high iron oxide contents to prepa-

re ceramic glaze pigments by Ovčačíková et al., (2021).

Obtaining glass-ceramics from urban and industrial was-

tewater sludge in Egypt by Garcia-Valles et al., (2011)

and the use of sludge from alumina extraction to manu-

facture glass and glass-ceramics (J. Yang et al., 2008) are

some examples of the use of sludge in arts.

However, the applicability of the sludge obtained from

the WWTPs depends on their composition and physico-

chemical characteristics, which in turn, depend on the

origin of the wastewater from the processes. Since Costa

Rica, which has an economy mainly dual, combines the

export area with the non-export sector (OECD, 2020),

both sides of the Costa Rican economy were chosen; be-

ing paint and metallurgical industry that correspond to the

first group and agricultural industry of the SME sector, to

identify which of these muds could be applied in artistic

expression either in sculpture or painting.

This article proposes to study the physicochemical cha-

racteristics of an environmental residue, such as the slu-

dge from some Costa Rican industries to propose it for

non-conventional artistic applications and mark a first

step so that in the future the School of Arts will be self-su-

fficient in producing basic supplies for its courses in a

sustainable way over time with environmental awareness.

Methology

Sample collection: Secondary sludge samples from la-

goons or oxidation tanks of three Costa Rican industries

were collected to determine their applicability in the ar-

tistic area. Companies that could potentially have a high

percentage of SiO

were selected, this compound being

of great added value in the vitrification or enameling pro-

cess, for this reason, paint, agricultural and metallurgical

industries were selected.

Humidity determination: The humidity of all the collec-

ted sludge was determined through gravimetry. For this,

the wet sludge was placed in an oven at 100 °C for a

period of 12 h.

Silicon Dioxide Percentage: The quantification of silicon

dioxide was carried out on a dry basis by gravimetry in

the Laboratory of Analytical Services (LASA), of the Es-

cuela de Química (School of Chemistry) of the Univer-

sity of Costa Rica, following their own established the

methodology.

Infrared spectroscopy: To obtain the bands of the func-

tional groups associated with the silicates, carbonates,

Yulök Revista de Innovación Académica, ISSN 2215-5147, Vol. 7, N.º 2

Junio-Diciembre 2023, pp. 64-74

Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

and oxides present in the sludge sample, a PerkinElmer

Frontier FT-IR-ATR model was used. Ten (10) scans per

sample were made with a large background to obtain the

final spectrum. The scan was from 4000 cm

-1

to 450 cm

-1

X-ray diffraction: A Brucker D8 Advance brand diffrac-

tometer with a LynxEye detector and a scan from 5° to

60° was used to identify the crystalline phases of the

components present in the sludge and thus determine the

ease of their separation/recovery.

Thermogravimetric analysis: A TGA equipment, TA Ins-

truments brand, model Q5000, with an inert atmosphere

was used using a heating ramp of 5 °C/min from 25 °C

to 600 °C, to study the behavior of the sludge concerning

temperature and identify volatile compounds and degra-

dations associated with silicates, oxides, and carbonates

of the mud.

X-ray energy dispersion spectrometry (EDS) and X-ray

fluorescence (XRF): To determine the elemental com-

position, a HITACHI model S3700-N scanning electron

microscope was used, where the X-ray fluorescence

technique was used (XRF) to detect the heavier metals

and X-ray dispersion spectrometry (EDS) to quantify

the lighter metals. The dried mud powders were placed

on a double carbon tape attached to a sample holder that

was inserted into the equipment and then a vacuum was

applied to carry out the measurements.

Results and discussion

The collection of sludge from lagoons and oxidation

tanks from different industries was carried out according

to Table 1 to determine the percentage of SiO

thus, to

know the potential that they would have in the process

of vitrification, ceramics, or sculpture at an artistic level.

The presence of SiO

is important within the structure of

vitrified ones because as it increases, the vitrified phase

increases, and in heavy metal-problem muds, polymeri-

zation of the silicate contributes to the chemical stability

of the metals in the matrix (Kuo et al., 2003, 2008).

In contrast, there are three categories of modern ceramics:

glass, glass ceramics, and engineering ceramics. Tradi-

tional ceramics fall under this last group and includes

everyday ceramics, sanitary and construction ceramics,

ceramics for arts and crafts, chemical ceramics, electrical

ceramics, and more. All of the aforementioned are prima-

rily made of natural silicates such as clay, quartz, felds-

par, or kaolin, where the SiO2 content is crucial to the

characteristics and final appearance of the ceramic (Ion,

2005; Zeng et al., 2021).

Sludge can be used as an addition to regular concrete ce-

ment for sculpture or it can be used to change the forge

or porosity of concrete mosaics (Armbruster, 2019; Ca-

mareno et al., 2006). The humidity in the sludge was also

measured, which was crucial because the processes of

transport and dehydration or drying require a lot of ener-

gy (Zhen et al., 2012). In this regard, the more moisture

there is in the sludge, the more challenging it will be to

adapt it for reuse and use in other applications. According

to Table 1, the agrochemical business, followed by the

paint industry, and the metal industry, which has the least

amount of water in the sample, are the ones with the hi-

ghest water content. This information helps characterize

the sludge and determine its potential for reuse because

the high moisture content in any material complicates its

transportation. After all, the right packaging and contai-

ner must be used. It is also important to consider that a

drying process requires a lot of energy, which increases

costs and makes the process more expensive.

The difference in moisture percentages is primarily attri-

buted to the sample collection method because the sha-

pe of the lagoon or oxidation tank influences the ease of

sample collection and, as a result, the amount of water

that is collected with it. Although these amounts are sig-

nificant, secondary sludges with moisture contents of up

to 99% have been reported (Canziani & Spinosa, 2019).

As it can be seen within the previous table, the paint in-

dustry is the one with the most elevated rate of silicon

dioxide on a dry basis, making the paint company the

one with the most noteworthy conceivable outcomes to

Table 1. Moisture percentage and silicon dioxide percentage of three sludge samples from different industrial processes

Source: Prepared by the authors

Industry Moisture Percentage (%) SiO2 Percentage (%)

Paints 26.5 ± 0.5 17.2 ± 0.2

Agrochemicals 30.5 ± 0.5 2.7 ± 0.2

Metals 14.3 ± 0.5 0.5 ± 0.2

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Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

be utilized in applications such as design or vitrification.

For this reason, it is that the slime from the paint industry

was chosen for the taking after characterization, in such a

way that its composition can be known and proposed for

pigments, paints or the like after appropriate treatments.

Two amassments of sludge from the paint industry were

then carried out, one in the low engendering season and

the other in the high engendering season, both were dried,

and the percentage of inorganic matter in them after dr-

ying was resolute.

In this case, it is carried out in the same way on a dry

basis and it is denoted that both batches have a similar

amount of inorganic matter, the one obtained in the low

season being greater according to Table 2.

Oxidation lagoons work to improve the microbial quality

of waters and decrease the oxygen requirement (BOD) by

the time they reach receiving waters; therefore, lagoon

design has traditionally focused on BOD removal, al-

though oxidation ponds important secondary functions of

sedimentation of organic and inorganic solids that carry

the process waters (Davies-Colley et al., 1995; Verbyla,

2016). When using the secondary sludge obtained from

the oxidation lagoons, the use of inorganic material is

present. That is the reason why when the season is low,

the water flow is lower and the industries, respecting the

water retention time to reduce the BOD, require more

time collecting wastewater. As a consequence, they also

store a greater amount of inorganic solids such as clays,

silicates, carbonates, etc. (Metcalf et al., 1991).

However, it is important to note that the difference be-

tween the data reported in Table 2 is very small, so it

could be considered that the inorganic matter in the paint

sludge samples is independent of the production season.

It should be noted that, since these are stable products

over time, the intention is to recover the inorganic com-

pounds since the organic compounds are mostly degraded

due to coming from an oxidation lagoon.

Next, the SiO

quantification process is perferomed be-

cause the inorganic matter is not only silicon but, it also

contains other oxides such as TiO

, CaO, K

O, and Al

among others, in their different phases. To do this, % SiO

is obtained separately for the batches and the entire ho-

mogenized sample. The results are shown in Table 3.

The percentage of SiO

is an important characteristic in

calcined sludge (without organic material) since a con-

siderable increase is shown for the sludge that contains

organic matter, thus going from 17.2 ± 0.2 to the data

reported in Table 3.

That SiO

in the paint industry specifically, is used as fi-

llers in the formulation which are added in powder and

work to generate body and volume in paint, change pro-

perties such as viscosity, and its final shine when it is dry.

(Carbonell, 2011, 2014) Therefore, it is natural that in

peak production season there is a higher amount of this

material. Also, as mentioned above, the SiO

content is

not only used in paints as it is also important when used

in vitrified or ceramics and that generates a wide range

of possibilities for using this residue by eventually reco-

vering it.

Regarding the characterization of the sludge, the Infrared

spectrum of the sample without organic matter is shown

in Figure 1, in which bands associated with the crystalline

phases shown in Table 4 can be observed.

Table 2. Percentage of inorganic matter in the selected sample.

Source: Prepared by the authors.

Painting Company Percentage of

inorganic matter (%)

Lot 1 (Low season) 50.5 ± 0.1

Lot 2 (High season) 49.5 ± 0.1

Table 3. Percentage of silicon dioxide of the selected sample.

Source: Prepared by the authors.

Painting Company SiO

(%)

Lot 1 (Low season) 43 ± 1

Lot 2 (High season) 50 ± 3

Homogenized sample 1 44 ± 3

Homogenized sample 2 37 ±1

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Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

The band, 3410 cm

-1

would correspond to water occluded

within the sample, and the band at 1079 cm

-1

to the stret-

ching of the Si-O bonds. While the bands 1417 cm

-1

, 874

-1

, and 711 cm

-1

correspond to the presence of carbona-

tes (Morales Acevedo & Pérez Sánchez, 2003).

Although these bands are the most notorious, it is impor-

tant to highlight that there are other functional groups in

the matrix whose bands are superimposed. The band at

796 cm

-1

corresponding to Si-O in the CaCO

/SiO

(Reig

et al., 2002) or TiO/SiO

mixtures, in addition to the band

at 960 cm

-1

corresponding to Ti

that can be substitu-

ted with Si

in the compound (Ren et al., 2008) it is not

shown, the same happens with the bands at 960 cm

-1

and

1060 cm

-1

corresponding to the Al-O bonds of the albite

(Feng et al., 2012).

Likewise, X-ray diffraction was used to determine the

phases of the main components obtained in it the values

of Table 4.

It is observed that the sludges are composed of various

crystalline phases, this makes sense considering that they

were extracted from oxidation ponds where mostly clays

are found that are chemically a combination of aluminum

and silicon with the general formula Al

·2SiO

·2H

and sometimes found as feldspar (K

O·Al

·6SiO

O·Al

·6SiO

), silicates in the form of quartz with

the formula SiO

, carbonates CO

and various metals

(Evans & Langdon, 1976; Zeng et al., 2021).

However, according to the thermogravimetric analysis

shown in Table 5, there is a first degradation correspon-

ding to the water occluded within the crystalline network,

which was visualized in the infrared spectrum of Figure

1 in the 3410 cm

-1

band. On the other hand, it has been

reported that the degradations between 600-750°C co-

rrespond to the dehydroxylation of Ca (OH)

, while at

750-850°C they are due to the decomposition of carbona-

tes into CaO and CO

, this due to the amount of calcium

contained in the sludge in the form of calcite (Rodríguez

et al., 2012; Segura Sierpes et al., 2016).

As previously mentioned, in Costa Rica the final disposal

of Sludge is regulated by current legislation; therefore,

it is essential to ensure that the chemical composition of

the sludge complies with parameters established by law.

For this, the complementary techniques of X-ray energy

dispersion spectrometry (EDS) and X-ray fluorescence

Figure 1. The infrared spectrum of the inorganic matter of the

sludge.

Source: Prepared by the authors.

Table 4. Crystalline phases detected by X-ray diffraction

Source: Prepared by the authors.

Crystalline phase Compound

Calcite CaCO

Albite NaAlSiO

Quartz SiO

Rutile TiO

Hematite Fe

Titanium and silicon oxide O

SiTi

Table 5. Study of degradation with temperature, through a thermogravimetric analysis.

Temperature Percentage of loss (%) Identity

0-200 °C 5.8 Occluded wáter

600-750 °C 10.8 Dehydroxylation (CaOH)

750-850 °C 0.1 CO

decomposition

Source: Prepared by the authors.

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Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

(XRF) are used. The first is used to determine the number

of light metals in the sample while the second is used to

quantify the heavier metals.

Results are shown in Table 6, it is important to emphasi-

ze that in the XRF technique, when visualizing only the

heaviest fraction, the percentage calculations are made

according to the quantity and sensitivity of elements that

can be visualized, hence the difference in the data for

each frame.

In this instance, Table 6 demonstrates that only Chro-

mium (Cr) might be detrimental if oxidized among the

components found by EDS; nevertheless, the concentra-

tion is not as high as that demonstrated in the majority of

elements, among which titanium, aluminum, and calcium

are also present in addition to silicon. Copper and zinc

are present in trace amounts when the elemental compo-

sition is examined using the XRF technique, particularly

copper, which has a value of 0.05 to 0.01%.

It is also known from mapping the sample that the dis-

tribution is homogeneous for each of the metals with the

largest percentage of importance, which is crucial when

carrying out recovery methods and purification of the slu-

dge components to enable their reuse. A homogenization

process had to be performed on each sample collected to

have a sample as a whole and verify whether the sample

had a homogeneous content or if it was segmented, de-

pending on the level of homogenization performed. This

homogeneity is shown in Figure 2. It is important to note

that several collections were made at different times to

obtain the final sample.

Table 6. Percentage of the concentration of each component present in the sludge

Source: Prepared by the authors

Element

Technique

EDS (%) XRF (%)

C 4.70±0.20 9.9±1.7

O 43±4 32.0±2.0

Na 0.70±0.20 0.0±0.0

Mg 1.05±0.13 0.18±0.05

Al 8.51±1.4 3.49±0.06

Si 11.5±1.1 6.08±0.08

S 0.33±0.01 0.24±0.02

K 0.408±0.001 0.33±0.03

Ca NA 15.86±0.32

Ti 13.2±2.7 23.73±0.59

Cr 0.74±0.08 0.60±0.06

Fe 1.88±0.54 4.58±0.26

Cu NA 0.05±0.01

Zn NA 2.85±0.12

Figure 2. Mapping of metals by EDS

Source: Prepared by the authors

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Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

Since the calcined sludge does not contain enough SiO

to adequately vitrify and melt, it is not advised to use it

neat for vitrification applications based on the results

of the aforementioned characterizations, which reveal

a very complicated composition inside the mud matrix.

As it contains significant levels of titanium and silicon

oxide as well as albite, it might be utilized in items like

ceramics or enamels as an alternative (Carter & Norton,

2013). Or even the potential utility of each component if

the right acquisition strategy is used. Following the pri-

mary goal of developing a long-term sustainable path for

the School of Arts where there is a raw material that may

be used in numerous procedures.

For the sludge used and characterized, the scheme of the

possible recovery process is shown in Figure 3

When compared to the phases indicated in Table 4, the

data shown in tables and Figure 2 make sense. Due to

its low cost, non-toxic nature, and high refractive index,

titanium oxide has been a well-known pigment since the

19th century. Its use expanded after the prohibition on

lead pigment since it functions well as a white pigment

and is added to other colors as a filler in paint formulation

(Chen et al., 2022). Additionally, as Ti is more expensive

than other metals and since it makes up a bigger fraction

of the sludge than other metals, extraction and purifying

techniques can be suggested to reuse it as a pigment or a

burden. For this, digestion with sulfuric acid and subse-

quent centrifugation can be used (See Figure 3) (Khezri

et al., 2013), which will produce a concentration of TiO2

in the mixing matrix.

However, digestion with sulfuric acid not only increases

the concentration of Ti but also that of Al, which is ano-

ther of the elements that sludge contains the most as albi-

te. Since. according to literature, the best conditions for

extraction of Al from sludge is using a pH of 1 using sul-

furic acid or a pH of 13 using NaOH (Truong et al., 2021;

Van Truong & Kim, 2022), it is important to mention

that the extraction with sulfuric acid will be functional

to concentrate both Ti and Al, although an increase in the

concentration of metals such as Mg will also be shown.

Regarding the Ca present in the sludge, it is found as cal-

cite according to Table 4. This compound does not need

to be purified or extracted since CaCO

is used by itself

as a pigment (Learner et al., 2007) or within the matrix

as a catalyst to carry out reactions at high temperatures

to obtain other pigments, for example, derivatives of Cr

(Kwon et al., 2018; Long et al., 2021). Iron, chromium,

and zinc, which are used to make pigments, are among

Figure 3. Block diagram of the sludge recovery and separation process.

Source: Prepared by the authors

Yulök Revista de Innovación Académica, ISSN 2215-5147, Vol. 7, N.º 2

Junio-Diciembre 2023, pp. 64-74

Rodríguez, K., Jirón, E. y Hernández, V. Characterization of sludge from industries

for possible recovery in Arts.

the elements of aesthetic relevance that EDS and XRF

also reveal in addition to the aforementioned metals (Co-

rreia et al., 2007).

Iron can be recovered by different methods using diges-

tions with either hydrochloric acid, ammonium oxalate,

or nitric acid (Rasmussen et al., 1996; B. Yang et al.,

2021), whereupon it dissolves and is later precipitated as

an oxide or forms part of phosphate, in terms of use in

arts it is best to use it as oxide due to its reddish coloration

(Correia et al., 2007).

Chromium on the other hand can be recovered by similar

digestion methods; however, highly toxic soluble chro-

mates or dichromates would be produced. Therefore, an

alternative is a solid phase recovery at high temperatu-

re (≈1000 °C) using a carbonate as catalyst (sodium or

calcium carbonate) and an oxygen-rich atmosphere, in

such a way that sodium or calcium chromate is obtained

(Long et al., 2021) this alternative is useful in sludges

such as those treated in this article that they contain cal-

cite in their matrix since the catalyst must not be added

externally.

On the other hand, zinc (in the form of ZnO) is found in

the sludge because it was once used as a white pigment

instead of TiO

, for example in the works of Pier Paolo

Pasolini, where no traces of TiO

were found (Learner

et al., 2007). In the sludges analyzed, the amount of Zn

is found to a lesser extent than Fe, this element can be

extracted in the same way as Fe with HCl, however, a

ZnFe

compound will be formed, for which it is re-

commended to use sulfuric acid as it is more selective

between Fe and Zn (Vereš et al., 2012). Following the-

se extraction processes, when using sulfuric acid, Ti, Al,

and Zn can be recovered with traces of Mg, all of these

elements used in the formation of white pigments or as

fillers in the formulation (Correia et al., 2007).

Despite the matrix’s extreme complexity it may be seen

from this diagram that each material that is broken down

in the figure can be used as a product, avoiding the need

to collect many products that would increase the purif-

ying expenses for the final product. However, since the

major goal is to lead the way in the utilization of mate-

rials made from trash, you don’t want to sell each product

separately.

Conclusions

• The amount of SiO

in the sludge from the oxida-

tion lagoons of Costa Rican industries was calcula-

ted, and the results showed 17.2 ± 0.2% for the paint

industry, 2.7 ± 0.2% for the agrochemical industry,

and 0.5 ± 0.2% for the metal industry. This indicates

that the paint industries have a significant amount of

potential for use in artistic endeavors due to the high

SiO

content.

• The chemical characterization of the sludges re-

veals that they are secure because their matrix lacks

potentially harmful elements. However, it presents

metals like iron and copper that, if the right use path

is taken, can be employed as pigments.

• A usage plan that involves the recovery of tita-

nium, aluminum, and silicon oxides that can be utili-

zed in enameling or ceramics can be established due

to the sludge’s composition.

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