Preliminary analysis of steelworks residues and their application in a sandy soil

The steel residues application (SR) in sandy soils, under a proper handling management, can result in a benefits range, among which, the soil acidity correction. This study investigated the gralunometric composition of three slags and one exhaustion powder from a steel mill, in the municipality of Marabá-PA, in addition to the ability of soil pH correction. To identify the granulometric fractions were used number 8, 10, 16 and 18 mesh sieves. The pH correction experiment were made in factorial scheme, evaluated 3 doses of each RS (1.5 t ha-1, 2.0 t ha-1 and 2.5 t ha-1) in vases with Neosol, for 60 days. Residues from the steel refining (EAFS, LDS and EAFD) showed a particle size predominantly under 1.00 mm, and promoted pH values above to 7.0. The blast furnace slag obtained domain of particle sizes > 2.00 mm, with 77% of the material retained in the sieves, and their soil disposition promoted similar results to dolomitic limestone, used traditionally to pH correction in acid soils, representing an alternative in soil preparation. Others residues also showed the soil pH correction capacity, although the used dosages proved to be above the ideal, with values above 7 and alkalinity tendency. The necessity of an investigation of EAFS, LDS and EAFD residues dosage are essential to pH soil correction, in order to condition the soil to pH ranges considered ideals (6-6.5).


Introduction
Historically, the soil is considered one of the main bases of agricultural production (Jenny, 1980;Silva et al., 2018), among with the management techniques introduced by the man and the investment capital of agricultural sector (Reichardt & Timm, 2016). Its formation is closely related to the combined number of physical, chemical and biological factors, followed by the climate actions that interact and tend towards equilibrium (Lal & Stewart, 2019). Worldwide, its noticed a wide soils variety under distinct physical-chemical particularities (Brevik & Hartemink, 2010), highlighted the fertility and their granulometries .
In Brazil, sandy texture soils also have the denomination of light or dry soils (Schaetzl & Thompson, 2015), with an 8% predominance in the Brazilian territory, with distribution in the Cerrado biome, specifically on the MAPITOBA region, which cover the states of Maranhão, Tocantins, Piauí and Bahia (Lumbreras et al., 2015;Bolfe et al., 2016), under dominance of Quartzarenic Neosols and small portions of Latosols and Argisols (Donagemma et al., 2016).
In general, Cerrado soils are highly weathered, of high depth and good drainage, but of precarious natural fertility (Fryrear, 1990;Lopes & Guilherme, 2016;Centeno et al., 2017;Gomes et al, 2019). The sandy fraction can represent up to 70% of the composition and its granulometry variated between 0.05 and 2.00 mm (Santos et al., 2019), resulting in high permeability, an important property when observing the groundwater contamination risks (Benghalia et al., 2015).
When the basic cations release rate is exceeded by their removal, the soil pH decreases, resulting in acid soils to the environment (Chenu et al., 2018). Cerrado soils pH has values in the 4.3 to 6.2 range, resulting in classes considered as medium (pH>5.0-5.9) and high acidity (pH <5.0) (Carvalho et al., 2009;Hunke et el., 2014;Lopes & Guilherme, 2016;Rodrigues & Silva, 2020). In Brazil, around 70% of the territory is composed by lands in excessive or moderate acidity (Sumner & Noble, 2003;Xu et al., 2020).
Sandy soils at pH ≤ 5.5 have the peculiarities of being toxics and inappropriate for agriculture when the potential acidity cause by the high Al 3+ saturation is related to low capacity of cations exchange (CTC) and Ca-Mg-K leaching (Lopes & Cox, 1977;Hunke et al., 2014;Reichert et al., 2016). The increase of Al 3+ rates in acid soils is a reflection of the hydrogen performance (H + ) over the low activity minerals, as kaolinite for example (Al4(Si4O10)(OH)8), releasing the Al 3+ ions that are retained on the negative charges of clay particles, tending to balance (Yong, Nakano, & Pusch, 2012).
Considering the mentioned aspects, among others, these soils show low relevance for agriculture, since the low nutritional rate and the susceptibility to erosion from wind and rain, result in difficulties in soil preparation and increases the spends with correctives and fertilizers (Fryrear, 1990;Colazo & Buschiazzo, 2015;Ferreira et al, 2017;Verruijt, 2018).
The pH correction and the increment of macro and micronutrients to the soil, are common practices and indispensable in the current agriculture (Crespo-Mendes et al., 2019). Wood ashes, marl, hydrated lime (Ca(OH)2) and the calcitic (CaCO3), dolomitic (CaMg(CO3)2) and calcined (CaO) limestones are considered the most frequent materials used for this purpose (Brady & Wile, 2013). In sandy soils, the liming associated with the use of Nitrogen-Phosphorus-Potassium (NPK) fertilizers is considered a managerial practice of great agricultural effectiveness, having as benefits the increase of water retention capacity (Esper Neto et al., 2019), the H + ions neutralization, reduction of Al 3+ and Fe 2+ and availability of P, K and S to the soil (Centeno et al., 2017;Li et al., 2019).
The steel industry, currently, is characterized as an activity which requires a large amount of matter and energy for the production of steel in different specifications, which has been accompanied by a diversified origin of solid residues, liquids or gaseous effluents (Liubartas et al., 2015;Gomes et al., 2016;Pulin et al., 2019). In 2019, Brazilian steel producing companies generated a total of 18 million tons of residues, distributed in Mud (4%), fine aggregate (6%) and Blast-furnace Slag (39%) and steelwork (26%) (IAB, 2020).
The application of these steel residues in sandy soils still needs researches (Ghosh & Ghosh, 2020), which can elucidate the behavior of the elements in the soil matrix as well as their percolation, since that, they can cause impacts in the ecosystem trophic chains, due to bioaccumulative heavy metals presence and soil high salinity presence (Chand, Paul, & Kumar, 2015;Mena et al., 2020).
In this sense, the hypothesis of the study were: (1) the steel residues has the capacity of pH correction of an acid soil; (2) residues with higher reactivities in the soil have a high charge of materials in its composition. Therefore, the objective of this article was to investigate preliminarily the physical-chemical properties of steel residues and their capacity of pH correction, when applied on a sandy soil.

Research characterization
The method applied to the study was hypothetical-deductive, with the presentation of the problem followed by hypotheses formulation for the searching of possible results, by observing and experimenting about the steelworks residues applied in a sandy soil (Marconi & Lakatos, 2017). The research obtained quantitative coverage under applied nature, with Research, Society and Development, v. 10, n. 5, e17910514520, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i5.14520 4 explanatory and experimental characteristics, which aim to provide greater familiarity of aspects with the object of study, as described in the four steps of figure 1 (Gil, 2018).

Study Area
The experiment was conducted between the months of 2019 March and April, on the Laboratory of Bioproducts and Biomass Energy (LABBIM), with localization in Pará State University, in the municipality of Marabá -Pará.

Experimental Design
The experimental units were constituted by plastic vases with 500 mL capacity, composed by a sandy soil of the Dystrophic Quartzarenic Neosol, according to Embrapa classification (2018), collected in the 0-20 cm depth. Physicalchemical properties are presented in the table 1.  The residues evaluated are from an integrated steel mill, composed by all steps in the steel production (figure 2). From the steel reduction process, the Blast furnace slag (BFS) was used, while from the refining was the electric arc furnace slag (EAFS), ladle furnace slag (LDS) and electric arc furnace dust (EAFD).

Steelworks residues on sandy soil
Bibliographic survey: Books and articles in Capes journals, ScienceDirect, ScIELO, Scopus e Springer. In addition to classification reports for steel residues and sandy soil. 1 Acquisition of materials: Sandy soil of the SINOBRAS forestry farm, steelworks residues, dolomitic limestone and plastic pots.
Experimental stage: Definition of the design followed by dosages of steelworks residues and dolomitic limestone.
Reviews: Measurement of the pH of the residues and their treatments according to step 3, followed by statistical evaluation.

RESIDUES Na
Ba At the time of collection, the residues were packed in inert polymer bags, according to NBR 10 007 (ABNT, 2004b), and submitted to pH analysis, according to NBR 10 006 (ABNT, 2004a), on the proportion of 250 g of residue in 1000 ml of distilled water resting for 7 days prior to reading, in triplicate.
At the end of the period, the pH value of the treatments were analyzed by the use of a LUCA-210 benchtop digital pH meter according to Teixeira et al. (2017), on the 100 g of soil to 250 ml of distilled water proportion, with a 1h rest before the measurement.

Statistical Analysis
The data of granulometric fractions and pH values were sequentially submitted to descriptive statistic, Shapiro-Wilk normality test (p>0,05), variance analysis and posteriorly the Tukey test at 5% of significance (p<0,05), using the IBM SPSS software, version 26 (IBM corp., 2019).

Results and Discussion
The table 3, presents the distribution of each steel residue by obtained fraction, where the blast furnace slag (BFS) showed 77% (384.84 g) of the material with granulometry greater than 2,0mm.
Subtitle: **not detected Averages followed by the same capital letters in the column and small letters in the same line do not differ from each other by the Tukey test at 5% of probability. BFS = Blast furnace slag; EAFS = Electric arc furnace slag; LDS = Ladle furnace slag; EAFD = Electric arc furnace dust. Source: Authors (2020).
The other residues, as detailed in table 3, exposed mainly granulometries lower than 1.00mm, being EAFD with 99% (499.33g), EAFS in 62% (311.88g) and LDS 49% (243.67g) of the material in 500 g corresponding to this fraction. The LDS and EAFD residues obtained granulometry from < 2.00 mm and < 1.18 mm, being detectable from these meshes, respectively. Furthermore, considering the intervals 2.00 -1.18 (table 3), the BFS(47.44 g) and EAFS (40.21 g) slag data were the only which do not differ statistically.
The steelworks residues granulometric determination in table 3, met the NBR 10 006 normative (ABNT, 2004a), which advocates values < 9.5 mm, therefore, it was not necessary to reduce the particle size of the materials, followed by them for pH analysis (figure 4). In figure 4, the pH values demonstrated high alkalinity of the different residues with LDS> EAFS> EAFD> BFS, and values between 7.83 for BFS and 12.59 at LDS. In addition, blast furnace slag (BFS) and electric arc furnace slag (EAFS) were the only residues to show pH values <10.Often, the physical-chemical composition of the steelworks residues is often usually quite heterogeneous, with the production model and the raw material used being the main factors of the alternation of values (Özbay, Erdemir, & Durmuş, 2016;Buzin, Heck & Vilela, 2017;Jiang, et al., 2018;Ghosh & Ghosh, 2020). The scrap used in the steelworks (reduction) has been the main input to electric furnaces, which demands higher concentrations of fluxes (CaO  Research, Society andDevelopment, v. 10, n. 5, e17910514520, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i5.14520 8 and MgO) in the process of separating impurities from the metallic alloy (Stathopoulos et al., 2013;Sadek, 2014 ;Alharahsheh et al., 2019). Teo et al (2020) highlights that the residues from steel refining sector (EAFS, LDS e EAFD) have more impurities when compared to those from the blast furnaces that produce pig iron (BFS), which reflects, particularly, in the formation of more amorphous and easily disintegrating material aggregates, and contributes to a smaller effectiveness of its granulometrics decrease in the ring mill. Residue finest fractions, results in materials with higher pH values, which in contact with the soil matrix, release hydroxyls in solution, in a way that alters the hydrogenionic potential , justifications that correspond to the presented values of granulometry <1.18 mm (table 3) (Deus & Büll, 2013;Sol-Sánchez et al, 2016). Nascimento, Brasil and Silva (2019) investigating the corrective effect of different doses and granulometries of slag in dystrophic yellow latosol verified that fractions lower than 2.00 mm promoted improvements in the soil chemical attributes compared to the conventional corrective, by raising the pH and provide nutrients.
Recommendations for the use of agricultural correctives are calculated based on the potentiality for total neutralization and reactivity of these compounds in the soil (Besen et al., 2021;MAPA, 2017). Studies aimed to define doses for steel residues use as correctives simulating the possible benefits, limitations to plant growth and its productivity, are essential since the reactive behavior of these in the soil has been shown to be quite variable (Deus & Büll, 2013;Deus et al., 2020).
The alkaline peculiarity of steel residues (figure 4), with use above what is recommended, can result in an increase in pH in the soil, and may even cause environmental damage (Scattolin et al., 2021), as was verified in patios with slag deposits . Studies with application of electric arc furnace slag influenced in the Canavalia ensiformis DC. (Feijãode-porco) growth, with low biomass production in alkaline soils (pH > 7) (Oliveira & Souza, 2020). It is noteworthy that EAFS residue of the authors had similar pH values in the soil (figure 5) with dosages greater than 30 mg dm -3 (pH = 7.00 -8.73), with the residue from the same origin of the productive process.
An analysis performed by Seh-Bardan et al (2013) demonstrated the equal doses or higher than 2% of EAFD raised the soil pH to level above of the intended, inhibiting the sorghum growth (Sorghum bicolor L.), with decrease of biomass production, increasing the salinity and critical loads of potentially toxics elements (Fe, Mn, Zn, Cu, Cd and Pb) in the soil.
These results matches with data obtained in the present study (figure 5), which the EAFD doses equal to or greater than 1.5 t ha -1 resulted in high pH values (higher than 7.64). Rocha et al (2019) in a study about EAFD doses in sandy soil, observed that leaching rate (TL) of underground water is inversely proportional to the residue concentration and that the micrometric granulometry facilitated the material reactivity, with the increase of soil alkalinity (pH > 7.5). To know the infiltration rate and the porosity changes in steel treated soils is important, since that drainage changes, aeration, infiltration profile can influence the mobility and elements availability .
Balancing density with porosity in sandy soils promotes improvements in water retention and minimizes the nutrients loss by leaching (Nunes et al., 2020). The conventional agricultural correctives presented textures between 0.15 and 0.30 mm, with predominance lower than 2.0 mm (Brady & Weil, 2013). This granulometric characteristic answers for a large part of the compound corrective action, as it determines the contact surface (specific surface) between the corrective substance and the soil fractions, which in turn interferes with the dissolution and neutralization power (Verruijt, 2018;Wang et al., 2020).
The excessive use of agricultural correctives in light soils, influences in the total filling of porous spaces, resulting in the decrease of water infiltration rate, reduction of gas exchanges (O2 e CO2) and erosion susceptibility (Yong, Nakano, & Pusch, 2012;Crespo-Mendes et al., 2019). Physical degradation of these soils is resulting from the shear tension and consequently the increase of soil surface flow (Bayat & Ghalandarzadeh, 2018). Cunha et al (2014) highlight that salinity is intrinsically related to the increase in soil pH and CTC, which favors the retention of potentially toxic elements in the surface layers (Ning et al., 2016). This behavior also points out to the care with the use of steel residues in agriculture, due to the presence of toxic metals that can inhibit microbial activity and root growth (Wan et al, 2019;Mena et al., 2020.). Acosta et al (2011) points out that soil with pH greater than 7, are susceptibles to low mobility and bioavailability of the metalic ions Cu 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Cr 2+ , Co 2+ , Pb 2+ and Cd 2+ , making difficult the plant absorption. In this aspect, the behavior observed by BFS was appropriate to the soil correction of agriculturable areas. On the other hand, the proportions of EAFS, LDS and EAFD showed elevated, requiring tests with doses lower than 1.5 t.ha -1 .

Conclusion
The steelworks residues presented granulometry characteristics and pH correction capacity compatibles to the conventional agricultural correctives. Among the analyzed residues, the blast furnace slag promoted equal results to dolomitic limestone, which may represent a lower cost alternative in soil preparation.
New tests evaluating lower dosages of EAFD, EAFS and LDS residues, or even a possible chemical adaptation prior to its use, are necessary to investigate the correction effects and soil protection, as the heavy metal accumulation, salinity increase and biodiversity maintenance.