Acid mine drainage (AMD) is the process resulting from the oxidation of sulfides exposed to the action of oxygen and water. The characterization of the minerals likely the formation and neutralization of AMD is important for the follow and evaluation of environmental impact. The analysis of X-ray diffraction (XRD) together with the Rietveld method is presented as a promising alternative to favor the identification and quantification of mineral phases. The results of the static test ANC achieved by accounting for carbonates consumed during the test, were correlated with the results obtained by the characterization techniques of X-ray diffraction (XRD) combined with the Rietveld method. The highest concentration of carbonate buffering found in AM2E, which may explain the static test results to be neutralizing for the sample. The major phases identified for both samples were aluminosilicates and quartz, with greater than 70% by weight levels.

1. Characterization of mining tailings containing sulfides and
carbonates applying XRD Rietveld method before and
after static tests
J. P. Arantes2
, P. R. Perdigão de Paiva2
, C. L. Caldeira1
, A. M Ferreira1,2
1
Instituto Nacional de Ciência e Tecnologia em Recurso Mineral, Água e Biodiversidade -
INCT-ACQUA
2
Centro Federal de Educação Tecnológica de Minas Gerais, Departamento de Engenharia de
Materiais, MG, Brazil
e-mail: judarantes@yahoo.com.br
Abstract:
Acid mine drainage (AMD) is the process resulting from the oxidation of sulfides exposed to
the action of oxygen and water. The characterization of the minerals likely the formation and
neutralization of AMD is important for the follow and evaluation of environmental impact.
The analysis of X-ray diffraction (XRD) together with the Rietveld method is presented as a
promising alternative to favor the identification and quantification of mineral phases. The
results of the static test ANC achieved by accounting for carbonates consumed during the test,
were correlated with the results obtained by the characterization techniques of X-ray
diffraction (XRD) combined with the Rietveld method. The highest concentration of
carbonate buffering found in AM2E, which may explain the static test results to be
neutralizing for the sample. The major phases identified for both samples were
aluminosilicates and quartz, with greater than 70% by weight levels.
Keywords: Rietveld Method, XRD, AMD, Acidification Potential
Introduction
The characterization of samples of sterile and wastes from mining favors the chemical
identification and quantification of the analyzed material, which may contribute to the
prediction of the potential for generation of AMD, it also aids in improving techniques used
for such. With that associated with the XRD Rietveld method has shown to be effective to
fulfill the needs for quantifying the mineral phases of the samples. The knowledge of the
mineralogical composition of the material contributes to the planning of actions in order to
prevent environmental degradation caused by mining activity. The ANC test is designed to
evaluate the potential acidity (AP) formation and neutralization potential (NP) of acidity of
the samples. This study was done to characterize two sulfide samples by means of XRD /
Rietveld tests to evaluate the speciation of carbonated phases of the samples and then
correlated with the neutralization and acidity potential obtained by the static test ANC.
Experimental Procedure
Natural samples are from Minas Gerais, in which AM1R is a sample of sulfide waste from
mineral processing and AM2E is a sample of sterile of rock. The XRD analyzes, the powder
method, were carried out under the following conditions: Cu Ka radiation (35KV / 40mA),

2. speed of goniometer 0.02 ° in 2θ per step, with counting time of 5 seconds per step and
collected in the range angle of 5 ° to 85 ° 2θ. The interpretation of the spectrum was
performed by comparison with standards contained in the database of ICDD. For the Rietveld
refinement, the GSAS program and EXPGUI interface profile function pseudo-Voigt
Thompson-Cox-Hastings and the background radiation adjusted by polynomial Chebyschev
was used. The procedure for the ANC test is described in detail in the study Stewart et al.
(2003). The test involves digesting 2 g of the sample pulverized in HCl, in this step the mix is
heated with HCl. After digestion, the solution is titrated with NaOH and then added two drops
of H2O2. After this procedure, the titration goes on to determine the amount of HCl consumed.
Results and Discussion
The criterion for evaluating the results of NP and AP is the ratio between the neutralization
and acidity potential, named of potential neutralization ratio (NPR) and the other criterion is
the NNP, which is the subtraction between NP and AP. A value less than 1 NPR implies a
sample acid-generating and greater than 2, acid-neutralizing. For the index NNP values <20
kg CaCO3/ton of material indicated that the sample is acid-generating and values > 20
CaCO3 kg/ton material indicates that the material is acid-neutralizing. The results of the
acidity potential (AP), neutralization potential (NP) of the sample are in TAB. 1.
Table 1 - Presentation of ANC test results
Ensaio Estático ANC
Sample % S -
Sulfetos
AP (kg
CaCO3/ton)
NP (kg
CaCO3/ton)
NNP (kg
CaCO3/ton)
NPR =
(NP/AP)
AM1R 0,94 29,38 19,36 -10,02 0,66
AM2E 1,53 47,81 69,35 21,54 1,45
The TAB. 1 showed the AM1R sample presents a value of NNP in the range of uncertainty
about the potential to generate acidity. On the other hand, the value of the NPR classified as
potentially generating acidity. For AM2E sample, the value of NNP points to the range that
classifies it as potentially neutralizing. However, NPR value is found within the uncertainty
zone. Figure 1A and 1B showed that the two samples were similar phases.
Figure 1: Diffractogram X-ray and Rietveld Refinement (a) AM1R; (b) AM2E.
These minerals are characteristic of rocks and soils that make up the sulfide gold ore coming
from MG. The presence of pyrite in these two samples is indicative that this material presents
1A 1B

3. the potential to form acid drainage. In contrast, the presence of carbonates, calcite in AM1R
and calcite and ankerite in AM2E may contribute to the natural neutralization of the acidity.
As verified in Tab. 2, the main minerals of the samples are quartz and muscovite. Carbonates
have been found in proportions greater than 7 wt% for both samples. However the siderite
does not contribute to the neutralization of generated acid and was found in AM1R. Pyrite
was found in low concentrations, about 1 wt%. The AM2E sample showed higher
concentration of carbonates calcite and ankerite.
Table 2 – Apresentação das quantificações do MR das amostras.
Fases
% em Massa Fases % em Massa
AM1R AM2E
Quartzo 30,9 Quartzo 30,8
Moscovita 45 Moscovita 35,9
Clorita 6,8 Clorita 8,6
Caulinita 4,6 Ankerita 6,7
Ankerita 3,3 Calcita 0,7
Calcita 0,8 Albita 5,4
Albita 5,6 Actinolita 10,2
Siderita 2,3 Pirita 1,7
Pirita 0,7
The quality index refinement of the samples AM1R were X2
=3,7; Rwp = 6,8; RBragg = 2,9 and
for AM2E were X2
= 4,3; Rwp = 7,5; RBragg = 3,8, indicating that the refinements were
performed properly to enable reliable analysis of crystal structures.
Conclusions
Applying the technique of XRD associated with Rietveld method was essential to know the
mineralogy of the material, which compared with the results of static tests allowed to evaluate
the potential formation of AMD, providing grants for actions to prevent possible
environmental damage.
Acknowledgments
This work was supported by CNPq, CAPES and INCT-Acqua.
References
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of technologies for avoidance and remediation of acid mine drainage: acid drainage
technology initiative. Virginia: ADTI, 1998. 140p.
2. RIETVELD, H. M. Aprofile refinament method for nuclear and magnetic structures. J.
Appl. Cryst. 2, p.65-71. 1969
3. Stewart, W., Miller, S.; Smart, R.; Gerson, A.; Thomas, J.; Skinne W.; Schumann, R..
Evaluation of the Net Acid Generation (NAG) Test for Assessing the Acid Generating
Capacity of Sulfide Minerals. In: SIXTH INTERNATIONAL CONFERENCE ON ACID
ROCK DRAINAGE. Australia. 2003. Proceedings…Cairns, p. 617-625.