pics

Anti icing equipment built into the plane. That's accomplished via a few different methods. An important distinction is that deicing is removing ice that has already formed, where as anti-ice prevents new ice formation. Most deicing options are only able on the ground, so it's important to have anti ice up and running before major accumulations occur.

1. Hot air from within the engine (bleed air) is piped to areas needing heat. This is used a lot for wing leading edges.
2. Resistive electrical heating - essentially a space heater. Used for smaller components like pitot tubes and fed by the engine's generator.
3. Mechanical removal via deicing boot. Essentially an expandable section of wing that breaks up already formed ice. Not super common.
4. Chemical melting done via alcohol spray for windscreens or deice spray for the outer skin. Pretty straightforward.
5. Altitude change. Moving to warmer, dryer air layers can work to melt built up ice, or prevent new ice formation, respectively. Flying high can also help, since the low air pressure allows ice to sublimate.
6. Avoiding flying into icing conditions. This one seems kind of obvious, but it's worth saying.

According to the ATC recordings, the FO reported that they were using their anti ice. Unfortunately, anti ice can only handle so much, and it seems like they may have ended up in conditions that overwhelmed their ability to prevent it. They tried to go to a higher altitude to escape the icing, but it obviously came too late. Ultimately, that'll be for the NTSB to decide what the root causes were. Hopefully the FDR survived by some miracle.