  The iron composition of globular clusters (GCs) is homogeneous in all but a
few massive clusters, despite the presence of multiple stellar populations.
Hence, most if not all the supernovae (SN) ejecta was not used to form stars.
Here by means of semi-analytic and numerical studies we address this issue
considering both stellar winds and supernovae feedback during the early
evolution of proto-globular clusters. We calculate the ability of stellar winds
to form a global wind that removes the gas left over from star formation. The
innermost radius from which such a global wind can be formed, the superwind
radius $R_{SW}$, is a function of the cloud parameters and the star formation
efficiency. In the case of complete gas expulsion ($R_{\textrm{SW}}=0$), the SN
ejecta merge with shock-heated winds and exit the cluster. On the other hand,
when $R_{\textrm{SW}}>0$, supernova remnants (SNRs) become pressure-confined if
evolving within a critical radius $R_{\textrm{blow}}$, and mix their products
with the residual gas. However, outside of this central zone the SNRs
experience blowout. In such cases, the thermalized ejecta escapes the cluster,
making the SN products unavailable for the formation of new stars. We estimated
the metallicity enhancement ($\Delta\textrm{[Fe/H]}$) of the leftover gas and
discuss the conditions required to produce secondary stellar populations with
$\Delta\textrm{[Fe/H]}$ in the range observed in the majority of GCs.
