Chemical Sulfuric Acid Research Articles

Comportamento de concreto misto com materiais cimentícios suplementares sob ácido sulfúrico - uma revisão sistemática

ABSTRACT Supplying sewerage systems in cities and factories has a high cost, both for design, execution, and maintenance. Reinforced concrete exposed to the aggressive acids produced by wastewater microorganisms receives high costly coatings to avoid corrosion and impairment of structural functions. Thus, this systematic review had two main goals: (1) to identify the supplementary cementitious materials (SCM) that improve concrete resistance to chemical sulfuric acid attack (H2SO4) and (2) to describe the performed tests to access concrete resistance to H2SO4 in laboratory conditions. After careful analysis of scientific references collected on indexed bases, the study showed that the test methods used to appraise samples resistance do not follow a standard protocol, hindering quantitative analysis between distinct studies results. In general, concrete resistance to H2SO4 is evaluated by immersing concrete samples in high concentrated acid solutions and assessing its compressive strength and mass change on a 28 or 30 days base sequence. Using SCMs improve resistance to sulfuric acid, and binders made with silica fume had the best results. This review may encourage the creation of test protocols to assess the resistance of concrete to H2SO4 that allow further statistical analysis of the research results.

Bioleaching of Copper-Containing Electroplating Sludge

The recovery of precious metals from solid waste through bioleaching has become a research hotspot in recent years. Thus, in this study, different strategies, such as chemical sulfuric acid leaching and mixed consortium bioleaching, were adopted to extract copper from Copper-Containing Electroplating Sludge. The results showed that, compared to chemical leaching, bioleaching showed a much better performance. Indeed, copper bioleaching efficiency reached 94.3% on day 7 (21.1% higher than that of chemical leaching). The results also indicated that the process of bioleaching involved more mechanisms and reactions than that of chemical leaching. The SEM and EDX tests showed that the surface morphology of the sludge changed significantly after bioleaching, and that an insignificant amount of copper remained in the leached residues. Furthermore, the leached residues passed the characteristic leaching toxic test and thus can be considered as non-hazardous raw materials for the construction industry. Hence, adopting a mixed consortium leaching process to extract copper from Copper-Containing Electroplating Sludge will not only significantly reduce environmental pollution, but will also use metal resources more efficiently.

Study on corrosion mechanism of alkali-activated concrete with biogenic sulfuric acid

Two different types of sulfuric acid, chemical sulfuric acid (CSA) and biogenic sulfuric acid (BSA) produced by T.f bacteria (Thiobacillus ferrooxidans), were applied into the simulation of the corrosion of alkali-activated concrete (AAC). Compared with CSA corrosion, three sulfuric acid concentrations (pH = 1.1, 1.6 and 2.0) were used to study the degradation of AAC under the BSA corrosion. In this paper, the change of appearance, compressive strength, Ca2+ emission, the environmental scanning electron microscope-energy dispersive spectroscopy (ESEM-EDS), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) respectively were used to study the deterioration mechanism of AAC under BSA attack. The result of the experiment revealed that BSA was more corrosive to AAC than CSA. However, with the impact of different concentrations of CSA and BSA, the product of corrosion of the AAC was still mainly gypsum. Therefore, BSA merely accelerated the corrosion rate and did not transform the corrosion mechanism. Additionally, AAC less affected by bacteria, the degree of corrosion of the AAC is mainly influenced by the concentration of sulfuric acid.

Evaluation of accelerated degradation test methods for cementitious composites subject to sulfuric acid attack; application to conventional and alkali-activated concretes

The degradation of cementitious composite materials under chemical sulfuric acid attack has been widely investigated. The agglomeration of a global database of test results is complicated by the differing test methodologies employed in each study. As a result it is difficult to isolate the influence of individual test parameters and hence directly compare the relative performance of different cementitious material. In this study the existing accelerated test methodologies including: brushing, wetting and drying cycling, and increased concentration of sulfuric acid are investigated such that the influence of test methodology on degradation rate and microstructural performance can be identified. This approach is taken with the view of developing a common methodology for indicating the susceptibility of a given cementitious material in an aggressive environment. Rather than comparing the performance of individual materials this work aims to compare the influence of test methodology when applied to different materials.

Study on the degradation mechanism of sulphoaluminate cement sea sand concrete eroded by biological sulfuric acid

Two different types sulfuric acids, i.e. the biological sulfuric acid (BSA) produced by T.t bacteria (Thiobacillus thiooxidans) and chemical sulfuric acid (CSA), were applied to simulate the corrosion. The sulphoaluminate cement (SAC) and the sea sand were mixed to made the concrete. The mass loss, compressive strength, chloride binding rate, pH value and pore structure were measured in the process of corrosion. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were used to analyze the products of the reaction. It could be found that under the corrosion of sulfuric acid, the initial hydration products of SAC, including ettringite (AFt) and Friedels’ salt, were decomposed continuously and the main corrosion product was dihydrate gypsum. Under corrosion of BSA, the corrosion became more intense due to the influence of bacterial effect. Moreover, the corrosion of BSA was more severe than that of CSA, which was obvious in terms of mass loss, strength decline and pore structure. The BSA has a more negative effect on the performance of SAC concrete.

Bioleaching and selective biorecovery of zinc from zinc metallurgical leach residues from the Três Marias zinc plant (Minas Gerais, Brazil)

BACKGROUND Gradual depletion of high-grade ores for heavy metals has encouraged industries to search for alternative methods to recover metals. Wastes generated from metallurgical industries can be used as a secondary resource as it contains high concentrations of metals. RESULTS The bioleaching kinetics and biorecovery of zinc from Zn-plant leach residues (ZLR), collected from a currently operating Zn-plant in Tres Marias (Minas Gerais, Brazil) were investigated using sulfuric acid producing Acidithiobacillus thiooxidans (A. thiooxidans). Response surface methodology (RSM) with full factorial central composite design (CCD) was applied to optimize Zn bioleaching by A. thiooxidans. The experiments were performed by varying the initial elemental sulfur concentration (5–30 g L−1), pulp density (5–50 g L−1) and initial pH (3.0–4.0 pH units). More than 75% of Zn was extracted from ZLR by A. thiooxidans under optimized conditions (sulfur concentration 25.1 g L−1, pulp density 21.5 g L−1 and initial pH 3.3). The leaching efficiencies of culture supernatant (biogenic sulfuric acid) and chemical sulfuric acid were compared to understand the leaching kinetics. The Zn leaching kinetics of ZLR followed the shrinking core diffusion model. Zn was selectively recovered from the Fe-rich acidic bioleachate by biogenic sulfide precipitation. Fe was first removed (more than 85% of total Fe in the leachate) by adjusting the initial pH to 5.0, followed by selective Zn biorecovery. CONCLUSIONS Zn (>95%) was selectively recovered from Fe-depleted ZLR by biogenic sulfides (with 1:1, Zn:biogenic sulfide mass ratio). Biohydrometallurgy can be a potential alternative resource recovery strategy for the selective recovery of Zn from ZLR. © 2016 Society of Chemical Industry

Comparative analysis of biogenic and chemical sulfuric acid attack on hardened cement paste using laser ablation-ICP-MS

The aim of this study was to investigate the relative role of chemically and microbially derived sulfuric acid (H2SO4) corrosion on hardened cement paste representing a concrete binder. Cement stone disks were exposed to chemical H2SO4 (pH1.0 and 2.0) and biological H2SO4 (pH1.5–2.1). After 28days, the degree of damage was evaluated by common visual-physical parameters and laser ablation-ICP-MS as a novel evaluation tool to assess changes in elemental distributions. The results revealed a pH-dependent degree of damage. The 4mm thick disk at pH1.0 was completely corroded. For the disks exposed to biogenic and chemical H2SO4 at pH2.0 an intact core remained with a similar thickness of the corrosion layer (1.8–2.0mm) and sulfuric acid penetration depth (1.1–1.3mm). Since the elemental distribution was similar in the corroded layer independent of applying biological or chemical H2SO4, no obvious differences between the two acid attacks were revealed.

Self-compacting concrete: using limestone to resist sulfuric acid

Self-compacting concrete (SCC) is increasingly being used in precast concrete sewer pipes, water treatment facilities, industrial floors and foundations that are susceptible to biogenic and/or chemical sulfuric acid attack. Since the mixture design of SCC is different to that of normal concrete, the durability of SCC in such applications needs to be evaluated. In particular, SCC can incorporate proportions of limestone filler and different combinations of aggregates, which is believed to alter its resistance to sulfuric acid. Hence, this study aimed to investigate the resistance to sulfuric acid of various SCC mixtures incorporating different limestone material types, proportions and combinations. The study comprised 12 weeks of immersion of test specimens in 1, 3 and 5% sulfuric acid solutions with a maximum pH threshold of 3, 2 and 1, respectively. The study revealed that the resistance to sulfuric acid of SCC incorporating limestone materials was dependent on the degree of solution aggression. While limestone filler contributed to increasing the resistance of SCC to the moderately aggressive solution (3% sulfuric acid), it accelerated the rate of mass loss in the highly aggressive solution (5% sulfuric acid). The effect of fineness and particle size of limestone and the kinetics of corrosion reaction on the resistance of SCC to sulfuric acid was also highlighted in this study. Microanalysis conducted upon test termination elucidated the damage mechanisms, and it was shown that the change in compressive strength after exposure to sulfuric acid solutions was not a proper indicator for the surface deterioration of SCC in acidic media.

Influence of polymer addition on biogenic sulfuric acid attack of concrete

A simple and reproducible microbiological simulation procedure in combination with a chemical procedure was used to test concrete for its potential resistance towards biogenic sulfuric acid. Concerning fundamental aspects of the corrosion reaction, it was shown that particularly the penetration of H 2S inside the concrete crevices accelerated the corrosion process. The influence of different polymer types and silica fume additions on the resistance of the concrete samples was determined. The addition of the styrene acrylic ester polymer resulted in an increased resistance while the addition of the acrylic polymer or silica fume caused less resistant concrete. For the vinylcopolymer and the styrene butadiene polymer, no significant effect was observed on the resistance of the concrete samples. The results of the two different test methods confirmed the difference between corrosion due to purely chemical sulfuric acid and corrosion due to microbiologically produced sulfuric acid.

Chemical and microbiological tests to simulate sulfuric acid corrosion of polymer-modified concrete

In certain industrial activities sulfuric acid is used during the production process, which may cause degradation of concrete structures. Another important phenomenon where sulfuric acid is responsible for concrete corrosion is biogenic sulfuric acid corrosion, which occurs often in sewer systems. Because previous investigations have already pointed out the difference between purely chemical sulfuric acid corrosion and biogenic sulfuric acid corrosion two different tests were performed: a chemical test and a microbiological test. Five different concrete compositions were used in the tests, including a reference mixture with high sulfate resistant portland cement and four different polymer cement concrete with a styrene–acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer, respectively. The concrete composition with the styrene–acrylic ester polymer showed in both tests a higher resistance than the reference mixture while the compositions with the acrylic polymer and the styrene butadiene polymer had a lower resistance than the reference mixture. The concrete composition with the vinylcopolymer did not induce the same results in both tests. The results of the chemical test indicated a slight increase in resistance compared with the reference mixture while the opposite was noticed for the microbiological test.

Chemical, microbiological, and in situ test methods for biogenic sulfuric acid corrosion of concrete

Biogenic sulfuric acid corrosion is often a problem in sewer environment: it can lead to a fast degradation of the concrete structures. Since the involvement of bacteria in the corrosion process was discovered, considerable microbiological research has been devoted to the understanding of the corrosive process. Mechanical engineers have focused on experiments comparing the resistance of several concrete mixes against biogenic sulfuric acid corrosion. Because of a lack of standardised methods, different test methods have been used, and various parameters have been modified to evaluate the resistance of the materials. The research done on sulfuric acid corrosion of concrete can roughly be divided in three groups: chemical tests, microbial simulation tests, and exposure tests in situ. In this article, an overview of the recent developments in the test methods for biogenic sulfuric acid corrosion and the obtained results are presented. Possible differences between biogenic sulfuric acid corrosion and chemical sulfuric acid corrosion are delineated.

Biogenic and Chemical Sulfuric Acid Corrosion of Mortars

The biogenic corrosion of mortars by sulfuric acid-producing bacteria was simulated in a controlled breeding chamber. Calcium aluminate cement (CAC) as well as portland and blended portland cement mortars were tested. Growth conditions for bacteria were optimized in a way that accelerated the naturally occurring corrosion (worst case) by a factor of at least 24. After 12 months of incubation in the chamber the samples being tested could be clearly classified according to their resistance properties. CAC mortars were found to resist microbiologically induced corrosion significantly better than portland and blended portland cement mortars. Measurement of the amount of biogenic sulfuric acid on CAC and portland and blended portland cement mortars demonstrated a higher amount of acid on the latter. The more effective resistance of CAC mortars was explained by the higher neutralization capacity due to their chemical composition and the smaller production of biogenic acid. Chemical immersion tests in sulfuric acid at pH 2 also revealed better resistance properties for the CAC mortars. But the mortars could not be distinguished as well as in the biological test because the samples were all exposed to the same concentration of acid. It is concluded that predictions concerning the long-term behavior of mortars used in sewerage networks are only reliable on the basis of the biogenic simulation experiment because the different metabolic activities of sulfuric acid-producing bacteria inhabiting different materials should be taken into account. Chemical corrosion tests tended to overestimate the resistance properties of portland and blast furnace cement mortars.