You don't give any indication why you are getting large white spaces, that is not expected. As a possible aid I provide an example document using several figures. If you can modify this and add it to your question in a form that shows the problem you are having, someone would be able to suggest changes.

\documentclass[twocolumn]{article}
\usepackage{graphicx,float}
\raggedbottom
\begin{document}
\section{zzzz}
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
\begin{figure}[htbp]
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{A floating figure}
\end{figure}
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
\begin{figure}[htbp]
\centering
\includegraphics[width=\linewidth]{example-image-a}
\caption{Another floating figure}
\end{figure}
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
\begin{figure}[htbp]
\centering
\includegraphics[width=\linewidth]{example-image-b}
\caption{Yet another floating figure}
\end{figure}
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
\section{\raggedright A long appendix with non floating figures and no text}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image-c}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image-b}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image-a}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image-c}
\caption{H figure}
\end{figure}
\begin{figure}[H]
\centering
\includegraphics[width=.8\linewidth]{example-image}
\caption{H figure}
\end{figure}
\end{document}
\includegraphics
it only movesfigure
environments, and it moves figure environments only to prevent getting large white space at page breaks. As you have given no indication of your coding it is very hard to tell you what to change.*
form to make a 2-column spanning figure. Really unless you show an example document that shows your problem it is impossible to guess why you are having issues.