## 4 Discussion
### Statistical Evaluation of Geochemical Data
The geochemical explanation for PC1-4 (\(\sim\) 6% of the total variance), which contains Mg, K, and Rb, is more questionable. Nevertheless, as the only potassium phase present in all studied samples is illite, this component probably represents the clay mineral content of the mud. Illite structure commonly contains Mg in the octahedral position, while Rb replaces potassium [11]. As correlation coefficients of all REEs are very small with PC1-4, the clays probably do not play any role in REE accumulation. Finally, the common behaviour of As, P and W in PC1-5 (\(\sim\)5% of the total variance) conforms with their similar ionic forms (AsO\({}_{4}\)[3-, PO\({}_{4}\)[2-, WO\({}_{4}\)[2-) under highly alkaline pH conditions, which is typical in red muds. The main result of the first step of the principal component analysis is that there are essential and well identifiable geochemical processes, like an accumulation of the HFSE and the chalcophile elements as well as their minerals, which are independent of REE accumulation. Moreover, there is a well-defined set of elements; all appear in PC1-1 component, which seems moving together with the REEs (Table 2). That is, why in the second step of the PCA (PC2) only the elements listed in the previous PC1-1 are included. Here three main REE accumulating processes can be recognized (Table 3). In PC2-1 (\(\sim\)28% of the total variance) Ti, the light and some heavy REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) appear. Comparing this information with the results of the phase analysis, the Ti-phases (anatase, rutile, ilmenite, titanomagnetic) are responsible for this process. Partition coefficients between rutile, ilmenite, titanomagnetic and silicate melts (magma) of any compositions are extremely low as suggested by several experiments [12; 13]. Consequently, these refractory igneous Ti-minerals probably are not responsible for accumulating the REEs in the red mud studied, what for the only candidate is anatase. In PC2-2 (\(\sim\)27% of the total variance) Ni, Fe, V, Sc as well as the rest of the heavy REEs (Ho, Er, Tm, Yb, and Lu) are collected. Based on the mineralogical data, the main accumulators for this set of elements should be the Fe-phases, goethite, and hematite. These two minerals and especially goethite commonly have a prominent role in fixing the mobile REE already in laterites and bauxites [14; 15]. Other authors, like [PERSON] et al. [16] found that formation of the Fe-oxides is incompatible with the enrichment of REEs. [PERSON] et al. [17] report that in some bauxites from Greece Sc is mainly hosted in hematite, while there in the red muds goethite accumulates Sc with a concentration of about two times more than hematite. The variables with high correlation coefficient in the last component (PC2-3, \(\sim\)26% of the total variance) are Sr, -Ca, Al and a selected set of REEs (Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The signs for Ca and Al suggest that the accumulation tendencies of their host minerals are just the opposite that is when Al increases, Ca decreases and vice versa. Keeping also the phase analytical results in mind, carcinrite, the main Al-phase and calcite, the dominant Ca-phase tend to appear \begin{table}
\begin{tabular}{c c c c} \hline \hline
\begin{tabular}{c} Accumulation of Ti-phases \\ and the HFEE and Sc \\ Accumulation of carcinrite \\ and selected REEs; no calcite \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the first principal component analysis (PCA). separated in the pitfalls. As all REEs have a positive sign, similar to Al, cancrinite should host these elements, while calcite should not, opposite to the common observations [18]. Based on the two subsequent PCA calculation steps, numerous element accumulation processes act in the red mud deposit could have been explored, three of which are responsible for the accumulation of the REEs.