[Tex/LaTex] organize table with dcolumn

dcolumntables

I created this table. But, the text are not center. the columns are organized on decimal marker, but the space between columns are not correct. I don't understand the dcolumn packege.

   \documentclass[12pt,twoside,a4paper,openright]{report}
    \usepackage[portuguese]{babel}
    \usepackage[utf8]{inputenc}
    \usepackage[inner=3cm,outer=2cm,tmargin=2.0cm,bmargin=2.0cm, includefoot, includehead]{geometry}
    \usepackage{mathtools}
    \usepackage{booktabs, multicol, multirow}
    \usepackage{tabularx}
    \usepackage{dcolumn}
    \usepackage{layouts}
    \usepackage{makecell}
    \usepackage{threeparttable}

    \newcolumntype{d}[1]{D{.}{.}{#1}}
    \newcolumntype{,}{D{,}{,}{-2}}
    \newcommand{\mc}{\multicolumn}
    \newcolumntype{R}{>{\raggedleft\arraybackslash}X}
    \newcolumntype{L}{>{\raggedright\arraybackslash}X}
    \newcolumntype{C}{>{\centering\arraybackslash}X}

    \begin{document}

    \begin{table}[htbp]
      \centering
      \caption{Composição quimica (wt\%) dos GCC's originais e modificados.}
      \begin{threeparttable}
      \begin{tabularx}{\textwidth}{l*{6}{d{-2}}}
    \cmidrule[0.8pt]{1-7}
      \textbf{Composição}  & \multicolumn{2}{c}{\textbf{H60}} & \multicolumn{2}{c}{\textbf{H90}} & \multicolumn{2}{c}{\textbf{H90 E}} \\
      \textbf{química (wt\%)}          &  \multicolumn{1}{X}{\centering Original} & \multicolumn{1}{X}{\centering Modificado} & \multicolumn{1}{X}{\centering Original} & \multicolumn{1}{X}{\centering Modificado} & \multicolumn{1}{X}{\centering Original} & \multicolumn{1}{X}{\centering Modificado}  \\
     \cmidrule{1-7}
    \textbf{Carbonato} & \multirow{2}{*}{103,2 \tnote{\textdagger}} & \multirow{2}{*}{55,5} & \multirow{2}{*}{97,4} &  \multirow{2}{*}{55,9} & \multirow{2}{*}{98,5} & \multirow{2}{*}{64,3} \\
    \textbf{de cálcio} &  & &  &  & &  \\
    \textbf{Água} & - & 3,9 & 0,2 & 3,2 & 0,3 & 2,5 \\
    \textbf{Sílica} & - & 40,6 & - & 39,6 & - & 30,6 \\
    \textbf{Impurezas} & - & - & 2,4 & 1,4 & 3,9 & 2,6 \\
     \cmidrule[0.8pt]{1-7}
      \end{tabularx}
      \begin{tablenotes}
        \item[\textdagger] Erro de medição.
        \end{tablenotes}
        \end{threeparttable}
      \label{tg_tabela}
    \end{table}

Best Answer

I removed tabularx and reduced \tabcolsep a bit so that the table fits within the page:

 \documentclass[12pt,twoside,a4paper,openright]{report}
    \usepackage[portuguese]{babel}
    \usepackage[utf8]{inputenc}
    \usepackage[inner=3cm,outer=2cm,tmargin=2.0cm,bmargin=2.0cm, includefoot, includehead]{geometry}
    \usepackage{mathtools}
    \usepackage{booktabs, multicol, multirow}
    \usepackage{tabularx}
    \usepackage{dcolumn}
    \usepackage{layouts}
    \usepackage{makecell}
    \usepackage{threeparttable}

    \newcolumntype{d}[1]{D{.}{.}{#1}}
    \newcolumntype{,}{D{,}{,}{-2}}
    \newcommand{\mc}{\multicolumn}
    \newcolumntype{R}{>{\raggedleft\arraybackslash}X}
    \newcolumntype{L}{>{\raggedright\arraybackslash}X}
    \newcolumntype{C}{>{\centering\arraybackslash}X}

    \begin{document}

    \begin{table}[htbp]
      \centering
\setlength\tabcolsep{4pt}
      \caption{Composição quimica (wt\%) dos GCC's originais e modificados.}
      \begin{threeparttable}
      \begin{tabular}{ld{3.1}*{5}{d{2.1}}}
    \cmidrule[0.8pt]{1-7}
      \textbf{Composição}  & \multicolumn{2}{c}{\textbf{H60}} & \multicolumn{2}{c}{\textbf{H90}} & \multicolumn{2}{c}{\textbf{H90 E}} \\
      \textbf{química (wt\%)}          &  \multicolumn{1}{c}{Original} & \multicolumn{1}{c}{Modificado} & \multicolumn{1}{c}{Original} & \multicolumn{1}{c}{Modificado} & \multicolumn{1}{c}{Original} & \multicolumn{1}{c}{Modificado}  \\
     \cmidrule{1-7}
    \textbf{Carbonato} & \multirow{2}{*}{103,2 \tnote{\textdagger}} & \multirow{2}{*}{55,5} & \multirow{2}{*}{97,4} &  \multirow{2}{*}{55,9} & \multirow{2}{*}{98,5} & \multirow{2}{*}{64,3} \\
    \textbf{de cálcio} &  & &  &  & &  \\
    \textbf{Água} & - & 3,9 & 0,2 & 3,2 & 0,3 & 2,5 \\
    \textbf{Sílica} & - & 40,6 & - & 39,6 & - & 30,6 \\
    \textbf{Impurezas} & - & - & 2,4 & 1,4 & 3,9 & 2,6 \\
     \cmidrule[0.8pt]{1-7}
      \end{tabular}
      \begin{tablenotes}
        \item[\textdagger] Erro de medição.
        \end{tablenotes}
        \end{threeparttable}
      \label{tg_tabela}

\noindent X\dotfill X
    \end{table}

\end{document}
Related Question