I have some long equations in my document. I want to add some square brackets so it is clear how the main text flows.

Here is my code
\documentclass{article}
\usepackage{amsmath}
\usepackage{multicol}
\usepackage{lipsum}
\begin{document}
\begin{onecolumn}
\begin{multicols}{2}
\lipsum[2]
\end{multicols}
\begin{equation}
+long\;equation 1-2-3-4-5-6-7-8-9-..................=
\end{equation}
\begin{multicols}{2}
\lipsum[3]
\end{multicols}
\end{onecolumn}
\end{document}
